摘要:

THE ROYAL SOCIETY OF CHEMISTRY Journal of Materials Chemistry Scientific Editor Staff Editor Professor Anthony R. West Mrs. Janet M. Leader Department of Chemistry The Royal Society of Chemistry University of Aberdeen Thomas Graham House Meston Walk Science Park Aberdeen A69 2UE, UK Cambridge CB4 4WF, UK Assistant Editor: Mrs. F. J. O'Carroll Editorial Secretary: Miss J. E. Chapman Materials Chemistry Editorial Board , Anthony R. West (Aberdeen) (Chairman) C. Richard A. Catlow (London) David A. Rice (Reading) David A. Dunmur (Sheffield) Rodney P. Townsend (Bebington) H. Monty Frey (Reading) Allan E. Underhill (Bangor) John W. Goodby (Hull) Graham Williams (Swansea) John D. Wright (Canterbury) ~~ ~~~ International Advisory Editorial Board M.A. Alario-Franco (Madrid) D. Kohl (Aachen) K. Bechgaard (Copenhagen) M. Lahav (Rehovot) J. D. Birchall (Runcorn) A. J. Leadbetter (Daresbury) D. Bloor (Durham) P. M. Maitlis (Sheffield) A. K. Cheetham (Oxford) J. S. Miller (Wilmington) E. Chiellini (Pisa) P. S. Nicholson (Hamilton) M. G. Clark (Wembley) M. Nygren (Stockholm) P. Day (Grenoble) V. Percec (Cleveland) D. Demus (Halle) C. N. I?. Rao (Bangalore) 6. Dunn (Los Angeles) M. Ratner (Evanston) W. J. Feast (Durham) J. Rouxel (Nantes) A. Fukuda (Tokyo) R. Roy (University Park, PA) D. Gatteschi (Florence) J. L. Serrano (Zaragoza) A. M. Glass (Murray Hill) J. N. Sherwood (Glasgow) J. B. Goodenough (Austin) J. Simon (Paris) G. W. Gray (Poole) J. F. Stoddart (Sheffield) A.C. Griffin (Cambridge) S. Takahashi (Osaka) S-i. Hirano (Nagoya) G. J. T. Tiddy (Bebington and Salford) P. Hodge (Manchester) B. J. Tighe (Birmingham) H. lnokuchi (Okazaki) Yu. D. Tretyakov (Moscow) W. Jeitschko (Munster) R. J. P. Williams (Oxford) 0. Kahn (Orsay) R. Xu (Changchun) Journal of Materials Chemistry (ISSN 0959-9428) is published six times a year by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Transactions Ltd., Blackhorse Road, Letchworth, Herts SG6 1 HN, UK. NB Turpin Transactions Ltd., distributors, is wholly owned by The Royal Society of Chemistry. 1991 Annual subscription rate EC (inc.UK) fl75.00, USA $395.00, Rest of World f 195.00. Customers should make payments by cheque in stirling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11 003. USA Postmaster: send address changes to Journal of Materials Chemistry, Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11 003. Second Class postage paid at Jamaica, NY 11431. All other dispatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe. PRINTED IN THE UK. @ The Royal Society of Chemistry, 1991. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers.Professor A. R. West, Scientific Editor Mrs. J. M. Leader, Staff Editor Tel.: Aberdeen (0224) 27291 8 Tel.: Cambridge (0223) 420066 Fax: (0224) 272938 E-Mail (JANET): Telex: 73458 UNIABN G RSCI @UK.AC.RL.GB Fax: (0223) 420247 or 423623 Telex: 818293 ROYAL G INFORMATION FOR AUTHORS The Royal Society of Chemistry welcomes submission of manuscripts intended for pub- lication in two forms, Articles and Materials Chemistry Communications. These should describe original work of high quality dealing with the synthesis, structures, properties and applications of materials, particularly those associated with advanced technology.Art ides Full papers contain original scientific work that has not been published previously. How- ever, work that has appeared in print in a short form such as a Materials Chemistry Com- munication is normally acceptable. Four copies of Articles including a top copy with figures etc. should be sent to The Editor, Journal of Materials Chemistry; The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB44WF, UK. Materials Chemistry Communications Materials Chemistry Communications contain novel scientific work in short form and of such importance that rapid publication is war-ranted. The total length is rigorously restric- ted to two pages of the double-column A4 format. The manuscript will be returned for reduction if.this length is exceeded. For a Communication consisting entirely of text and ten references, with no figures, equations or tables, this corresponds to approximately 1600 words plus an abstract of up to 40 words. Submission of a Materials Chemistry Com- munication can be made either to The Editor, Journal of Materials Chemistry; The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK, or viaa member of the Interna- tional Advisory Editorial Board. In the latter case, the top copy of the manuscript includ- ing any figures etc., together with the name of the person to whom the Communication is being submitted, should be sent simultan- eously to the Editor at the Cambridge address. Authors may wish to contact the Board mem- ber to ensure that he is available to arrange review of the manuscript within reasonable time. In order to avoid delay in publication, proofs of Communications are not sent to authors unless this is specifically requested. Full details of the form of manuscripts for Articles and Materials Chemistry Communi- cations, conditions for acceptance etc. are given in issue number one of Journal of Materials Chemistry published in January of each year, or may be obtained from the Staff Editor. There is no page charge for papers published in Journal of Materials Chemistry. Fifty reprints are supplied free of charge. Any author who is publishing in Journal of Materials Chemistry for the first time is entitled to a free copy of the issue in which the paper appears.

ISSN:0959-9428    

DOI:10.1039/JM99101FX021

出版商:RSC    

年代:1991

数据来源: RSC

ISSN:0959-9428    

DOI:10.1039/JM99101BX023

出版商:RSC    

年代:1991

数据来源: RSC

ISSN:0959-9428    

DOI:10.1039/JM99101FP067

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

A.C. alignment Dielectric Relaxation Spectroscopy and Molecular Dynamics of a Liquid-crystalline Polyacrylate containing Spiropyran Groups Matrix Surface Modification by Plasma Polymerization for Enzyme Immobilization AcidityCorrelation of Surface Acidity with Electrical Conductivity of Silica-supported Heteropoly Compounds studied by the Complex-impedance Method Agar hydrogel Preparation of Ternary Composite Hydrogels of Agarose Concanavalin A and a Glycolipid Monolayer and their Permeation Properties Alkali-metal fluoride Alkali-metal Fluorides supported on ?-Alumina Alkali-metal salt Luminescence Properties of A,ReCI Crystals Alkenyl isocyanate Formation of Ordered Multilayers by Stepwise Oligomerisation Alkoxide. Sol-Gel Synthesis of Zr(HPO,),.H,O 681.Alkox ydithiobenzoate Synthesis and Phase Behaviour of Mesomorphic Transition-metal Complexes of Alkoxydithiobenzoates Linear Dichroism of Mesomorphic Transition-metal Complexes Alkylammonium iodide Mechanism of n-Alkylammonium Ion Intercalation into the Layered Host a-VOP0 2H20 Alk ylphthaloc yanine. Liquid-crystalline Zinc and Nickel 1,4,8,11,15,18,22,25- Octaalkylphthalocyaninates:Beneficial Effect of the Zinc Ion y-Alumina Alkali-metal Fluorides supported on y-Alumina Alumina hydrate Nuclear Magnetic Resonance Spectroscopy Investigation of Thermal Transformation Sequences of Alumina Hydrates. Part Thermal Transformation Sequences of Alumina Hydrates. Part Aluminium hydroxide Porous Cross-linked Materials formed by Oligomeric Aluminium Hydroxides and a-Tin Phosphate Aluminium silicate Chemical Vapour Deposition of Aluminium Silicate Thin Films I43 Amino acid Synthesis and Conformational Study of Cuticle Collagen Models Aminoferrocene Intercalation of 2-Aminoethylferrocene into the Layered Host Lattices MOO 2H-TaS and a-Zr(HPO,),.H,O Ammonium ion Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Ammonium ion reorientation Ammonium-ion Motions in the Hexagonal Tungsten Trioxide Framework Ammonium tungsten bronze Ammonium-ion Motions in the Hexagonal Tungsten Trioxide Framework Amorphous material Arylaldehyde and Arylketone Hydrazones as a New Class of Amorphous Molecular Materials Synthesis and Characterization of Isomeric Biphenyl-containing Poly(ary1 ether-bisketone)s.Part I. -Polymers derived from Anatase-rutile transformation. Promotion of the Metal-Oxide Support Interaction in the Nil TiO Catalyst Anisotropic conductivity Alkyl-substituted Oligothiophenes Crystallographic and Spectroscopic Studies of Neutral and Doped Forms Antiferromagnetism La -,S ,CUO - Structural Magnetic and Transport Measurements on Antiferromagnets Insulators and Superconductors Magnetic Frustration Spirals and Short-range Order in Cr,Fe -,V04-I Solid Solutions Antimonate New Antimonate-Vanadate with the Rutile Structure Antimony Synthesis and Crystal Structures of the Layered I-III-V Zintl Phases K,In,X where X =As Sb Antimony-doped tin oxide ceramic Infrared Reflectance Spectra of Sb-doped SnO Ceramics Aromatic polyether sulphone Synthesis of Aromatic Polyethers by the Scholl Reaction Aromatic polymer Aromatic Ether-Ketone-'X' Polymers Aromatic Ether-Ketone-'X' Polymers Part 2.-EK-Imide Copolymers Arsenic Synthesis and Crystal Structures of the Layered I-III-V Zintl Phases K,In,X where X=As Sb Arylaldehyde hydrazone Arylaldehyde and Arylketone Hydrazones as a New Class of Amorphous Molecular Materials Arylketone hydrazone Arylaldehyde and Arylketone Hydrazones as a New Class of Amorphous Molecular Materials Atomistic simulation Surface Segregation of Sr in Doped MgO Atomistic Lattice Simulations of the Ternary Fluorides AMF Auger electron spectroscopy Carbon Deposition on Iron-Manganese-Chromium Spinels Barium calcium copper oxide Synthesis and Structure of Ba,CaCU 06.96(CO3).Perovskite containing Carbonate Anions and Related Phases Beryllophosphate Synthesis and Crystal Structure of a Novel Beryllium Phosphate Open-framework Structure B.E.T. surface area Progress towards Preparation of High-surface-area Rare-earth Oxides Magnesium Oxide as a Support Material for Dehydrogenation Catalysts Binuclear complex Low-temperature Synthesis of Perovskite Solids LaM0 (M =Ni Co Mn) via Binuclear Complexes of Compartmental Ligand N,N'-Bis(3- arboxysalicylidene)ethylenediarnine Bioadhesive Synthesis and Conformational Study of Cuticle Collagen Models Biodegradation Synthesis Characterization and Biodegradation Test of Nylon Bipolar on Elastic and Coulombic Contributions to Real-space Hole Pairing BirefringenceHigh-birefringence Materials using Metal-containing Liquid Crystals. Synthesis of Aromatic Polyethers by the Scholl Reaction Bismuth Oxide Superconductor Phase Relations in the System BiO,,,-SrO-CuO at K Bismuth-samarium-oxygen system The Bi,O,-Sm,O System Phase Diagram and Electrical Properties Bis(phthalocyaninato)ytterbium( r) Electrochemical Salt Formation in Bis(phthalocyaninato)ytterbium(uI)-Stearic Acid Langmuir- Blodgett Films Bisphthaloc yanine Synthesis Structure and Spectroscopic and Electrochromic Properties of Bis(phthalocyaninato)zirconium(iv),29 Bi-Sr-Ca-Cu-0 system Metal-to-non-metal Transitions in High-temperature Oxide Superconductors monitored by Photoelectron Spectroscopy Bi-Sr-Ca-Cu-0 High-T Superconductors produced by using a Rapid Thermal Melt Processing Technique Bi-Sr-Cu-0 system Characterization of Ca-doped Bi +3r2 -xCuOz Phase Relations in the System BiO -SrO-CuO at K Bis(salicylaldehyde)copper(Ir) complex Paramagnetic Rod-like Liquid Crystals Bis[5-(4- Bistability Synthesis of a Crowned Azobenzene Liquid Crystal and its Application to Thermoresponsive Ion-conducting Films Boehmite Nuclear Magnetic Resonance Spectroscopy Investigation of Thermal Transformation Sequences of Alumina Hydrates Part Boron Trivalent Boron as Acceptor Chromophore in Asymmetrically Substituted 4,4'-Biphenyl and Azobenzene for Non-linear Optics Brownmillerite Investigation of Defect Ordering in the Perovskite System SrCr,,,Fe,,,O -y by Mossbauer Spectroscopy Cadmium selenide Growth of 11-VI Compounds by Metal-organic Chemical Vapour Deposition Cadmium sulphide Growth of 11-VI Compounds by Metal-organic Chemical Vapour Deposition Calcination Thermal Transformation Sequences of Alumina Hydrates.Part I. -Gibbsite y-Al(OH) Thermal Transformation Sequences of Alumina Hydrates. Part Calcium carbonate Oriented Nucleation of CaCO from Metastable Solutions under Langmuir Monolayers Carbon deposition Carbon Deposition on Iron-Manganese-Chromium Spinels Catalyst Characterization of Copper-Manganese Hydroxysalts and Oxysalts Copper-Cobalt Hydroxysalts and Oxysalts Bulk and Surface Characterization Magnesium Oxide as a Support Material for Dehydrogenation Catalysts Catalyst support Magnesium Oxide as a Support Material for Dehydrogenation Catalysts Catalyst synthesis Progress towards Preparation of High-surface-area Rare-earth Oxides Catalytic redistribution polymerisation Simple and Convenient Method for Preparing Functionalised Network Organopolysilanes Cation-radical polymerization Synthesis of Aromatic Polyethers by the Scholl Reaction Ceramic oxide Compound and Solid-solution Formation Phase Equilibria and Electrical Properties in the Ceramic System Zr0,-La203- Ta,Os Surface Segregation of Sr in Doped MgO Improved Method for the Determination of the Oxygen Content ChalcogenideAnalytical Characterization by X-Ray Photoelectron Spectroscopy of Quaternary Chalcogenides for Cathodes in Lithium Cells Characterization and Photoelectrochemical Studies of CuInS Thin Films Prepared by Sulphurization of Cu-In Alloy Charge transfer Effect of Composition of Polymer Backbone on Spectroscopic bipyridy1)-containing 4-Vinylpyridine/Styrene Copolymers Synthesis and Characterisation of [(q-C,Me,)Ru(p,q-CsMe5)Ru(q-C,Me,)]+[A]-; [A]- =TCNE TCNQ C,[C(CN),] Dielectric Relaxation Peaks in the Low-frequency/High- the Thermostimulated Depolarization Current (TSDC) Technique in 2,3,7,8-Tetramethoxychalcogenanthrenes-TCNQ Charge-transfer Complexes Chemical deposition Novel Chemical Preparative Route for Semiconducting MoSe Thin Films Chemical sensor Optical Properties of Sol-Gel Glasses doped with Organic Molecules Chirality Chirality in Liquid Crystals Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization.Part 13. -Synthesis and Living Cationic Polymerization of (S)-(-)-2-MethyIbutyl 4-(w-Vinyloxy)-Groups Correlation between Absolute Configuration of Benzylic Chiral Centre and Sign of Spontaneous Polarization of Chiral Dopants for Ferroelectric Liquid Crystals Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Chronoamperometric probe. Electrochemical Probing of the Sol-Gel-Xerogel Evolution Coating Zirconium Compounds as Coatings on Polystyrene Latex and as Hollow Spheres Low-temperature Vapour Deposition of High-purity Copper Coatings from Bis[N-(Fluoroalkyl)salicylaldiminato]copper Chelates Cobalt Electrodeposition and Study of Multilayered Co/Cu Structures Cobalt acetate Thermal Decomposition of Cobalt(i1) Acetate Tetrahydrate Thermogravimetric Analysis Cobalt oxide Thermal Decomposition of Cobalt(i1) Acetate Tetrahydrate Thermogravimetric Analysis Cobaltocene Single-crystal Conductivity Study of the Tin Dichalcogenides SnS -$ex Intercalated with Cobaltocene I Coexistence domain Phase Relations in the System BiO,,,-SrO-CuO at K Collagen Synthesis and Conformational Study of Cuticle Collagen Models Colloid Preparation of Uniform Colloidal Particles of Hafnium Compounds Zirconium Compounds as Coatings on Polystyrene Latex and as Hollow Spheres Columnar mesophase Alkyloxy-substituted CTTV Derivatives that exhibit Columnar Mesophases Columnar Mesophases of Cyclic Trimers of Disubstituted Acetylenes Complex impedance spectroscopy Correlation of Surface Acidity with Electrical Conductivity of Silica-supported Heteropoly Compounds studied by the Complex-impedance Method Computed conformation Semi-crystalline Alkali-metal Salt Complexes with Poly(o1igooxyet hyleneoxy- I ,2-phenylene)s Computer simulation Calculation of Structural and Defect Properties of a-U308,105 Computer-simulation Study of Alkali-metal Insertion.Conducting polymer Thermal and Electrical Conduction Studies on Polypyrrole Tetracyanoplatinate Novel conducting Soluble Co-polymers of Aniline Microstructural Studies on Polypyrrole Characterization of Conducting Polymer-Quartz Composites Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5-pyridine) Conductivity Single-crystal Conductivity Study of the Tin Dichalcogenides SnS2 -xSex Intercalated with Cobaltocene Conjugated polymer Non-linear Optical Properties of Group Metal Alkynyls and Copolymer Novel conducting Soluble Co-polymers of Aniline High-surface-area Resins derived from 2,3-Epoxypropyl Methacrylate cross-linked with Trimethylolpropane Trimethacrylate Radiation Chemical Yields and Lithographic Performance of Electron-beam Resists based on Poly(methy1styrene-co- Crystallization of Sparingly Soluble Salts on Functionalized Polymers Variation with Composition of the Intrinsic Sensitivity of Halogen-substituted Styrene Copolymers to Electron-beam Radiation Preparation and Characterization of wholly Aromatic para-Linked Copolyamides of Poly(p-phenyleneterephthalamide) CopperElectrodeposition and Study of Multilayered Co/Cu Structures Copper-cobalt oxysalt Copper-Cobalt Hydroxysalts and Oxysalts Bulk and Surface Characterization Copper-manganese oxysalt Characterization of Copper-Manganese Hydroxysalts and Oxysalts Copper(I1) complex Low-temperature Vapour Deposition of High-purity Copper Coatings from Bis[N-(Fluoroalkyl)salicylaldiminato]copper Chelates Synthesis and Thermal Behaviour of Mesomorphic Cu" Schiff's Base Complexes Coulomb interaction Madelung Energy and Hole Location in YBa,Cu,O Crosslinking High-surface-area Resins derived from 2,3-Epoxypropyl Methacrylate crosslinked with Trimethylolpropane Trimethacrylate Mesomorphic Behaviour of some Crosslinked Derivatives of All- Crosslinked Layered Materials formed by Intercalation of Octameric Siloxanes in Metal(1v) Hydrogen Phosphates Crowned azobenzene Synthesis of a Crowned Azobenzene Liquid Crystal and its Application to Thermoresponsive Ion-conducting Films Crystal growth Electron Microscopic Study of the Morphology of Lead Sulphide Growth Technique Crystallization of Sparingly Soluble Salts on Functionalized Polymers Oriented Nucleation of CaC0 from Metastable Solutions under Langmuir Monolayers Crystal morphology Electron Microscopic Study of the Morphology of Lead Sulphide Growth Technique.Crystal structure Synthesis Structure and Spectroscopic and Electrochromic Properties of Bis(phthalocyaninato)zirconium(Iv),29 Phase Transition of Tetrakis(octy1thio)tetrathiafulvalene(TTC,-TTF) and Crystal Structure Analysis X-Ray Crystal Structure of a Triazine Adduct of Dimethylzinc An Important Precursor for the Deposition of II/VI Materials Synthesis and Crystal Structure of a Novel Beryllium Phosphate Open-framework Structure Database Analysis of Crystal-structure-determining Interactions Metals Oxonol Dyes X-Ray Crystallographic and Solid-state 13C Nuclear Magnetic Resonance Studies of some Organic Semiconductors Synthesis and Crystal Structures of the Layered I-111-V Zintl Phases K,In,X where X =As Sb Second-harmonic Generation Properties of some Co-ordination Compounds based on Pentanedionato Ligands Crystal Structures of Chiral Smectogenic 4-Octylbiphenyl-4-y1 p-Methylheptyloxy]biphenyl-4-carboxylate,667 Synthesis and Characterisation of [(r Me,)Ru(p,q-C,Me,)Ru( -C5Me,)]+[A]-; [A]-=TCNE TCNQ C,[C(CN),]3 Crystal Structure and Pressure Dependence of Electrical Conductivities of [(CH,),N][Pt(dmit),12 Alkyl-substituted Oligothiophenes Crystallographic and Spectroscopic Studies of Neutral and Doped Forms Synthesis and Phase Behaviour of Mesomorphic Transition-metal Complexes of Alkoxydithiobenzoates Crystallinity. Semi-crystalline Alkali-metal Salt Complexes with Poly(oligooxyethy1eneoxy-1,2-phenylene)s Cu+ /?"-Alumina Electron Paramagnetic Resonance Spectroscopy of Cu +/Cu2 p"-Alumina CuInS Characterization and Photoelectrochemical Studies of CuInS Thin Films Prepared by Sulphurization of Cu-In Alloy Cyclic voltammetry Synthesis Structure and Spectroscopic and Electrochromic Properties of Bis(phthalocyaninato)zirconium(w) Electrochromism in Titanyl and Vanadyl Phthalocyanine Thin Films C yclotetraveratr ylene Alkyloxy-substituted CTTV Derivatives that exhibit Columnar Mesophases Dangling-bond site Nature of Dangling-bond Sites in Native Plasma-polymerized Films of Unsaturated Hydrocarbons and Electron Paramagnetic Resonance Kinetics on Heat Treatment of the Films Dealuminat ion Dealumination of Hexagonal Polytype of Faujasite by Treatments with Silicon Tetrachloride Vapour Decamethylmanganocenium 2,3-dichloro-5,6-dicyanobenzoquinoneide Novel Co-operative Magnetic Properties of Decamethylmanganocenium 2,3-Dichloro-5,6- dicyanobenzoquinoneide [Mn(C ,Me,),]' [DDQ] .-,479 Defect Investigation of Defect Ordering in the Perovskite System SrCr,,,Fe,,,O -y by Mossbauer Spectroscopy Calculation of Structural and Defect Properties of a-U308 Computer-simulation Study of Alkali-metal Insertion into Luminescence Properties of A2ReCl Crystals Defect Calculations in Solids beyond the Dilute Limit Dehydrox ylation Evolution of Structural Changes during Flash Calcination of Kaolinite Thermal Transformation Sequences of Alumina Hydrates.Part Flash Calcination of Kaolinite Mechanistic Information from Thermogravimetry Depletion layer Infrared Reflectance Spectra of Sb-doped SnO Ceramics Depth profile Depth Profiles and Electrochemical Properties of IrO Electrocatalysts Stabilized with TiO Dichroism Linear Dichroism of Mesomorphic Transition-metal Complexes Dielectric relaxation Dielectric Relaxation Spectroscopy and Molecular Dynamics of a Liquid-crystalline Polyacrylate containing Spiropyran Groups Dielectric Relaxation in Hydroxypolyesters Dielectric Relaxation Peaks in the Low-frequency/High- the Thermostimulated Depolarization Current (TSDC) Technique in 2,3,7,8-Tetramethoxychalcogenanthrenes-TCNQ Charge-transfer Complexes Differential scanning calorimetry Vitrification in Low-molecular-weight Mesogenic Compounds Dimethy lquaterthiophene Alkyl-substituted Oligothiophenes Crystallographic and Spectroscopic Studies of Neutral and Doped Forms Dimethylzinc X-Ray Crystal Structure of a Triazine Adduct of Dimethylzinc An Important Precursor for the Deposition of II/VI Materials Diol complex Diol-based Sol-Gel System for the Production of Thin Films of PbTiO Dioptase Formation of Q8M,o([(CH,),SiO],oSiao,,> from QM4([(CH3),Si0I4Si} Olivine and Dioptase Dispersion Dispersion of Silicon Carbide Whiskers and Powders in Aqueous Electrical conductivity Crystal Structure and Pressure Dependence of Electrical Conductivities of [(CH 3)4N] [Pt(dmi t),] ,,827 Electroactive polymer.Scanning Tunnelling Microscopy Study of Osmium-containing Electroactive Metallopolymer [0 (bipy),(PVP) Cl]Cl Films Electrocatalyst Depth Profiles and Electrochemical Properties of IrO Electrocatalysts Stabilized with TiO X-Ray Diffraction Characterization of Iridium Dioxide Electrocatalysts Behaviour of the Adsorbed C1' Intermediate in Anodic C1 Evolution at Thin-film RuO Surfaces Electrochemical cycling Scanning Tunnelling Microscopy Study of Osmium-containing Electroactive Metallopolymer [Os(bipy),(PVP),,Cl]CI Films Electrochemical reduction Room-temperature Electrochemical Reduction of YBa,Cu,O -x Electrochemical salt formation Electrochemical Salt Formation in Bis(phthalocyaninato)ytterbium(rII)-Stearic Acid Langmuir- Blodgett Films Electrochromism Electrochromic Nb20 and Nb,O,/Silicone Composite Thin Films prepared by Sol-Gel Processing Sol-Gel Synthesis of WO Thin Films Electrochromism in Titanyl and Vanadyl Phthalocyanine Thin Films Electrochemical Salt Formation in Bis(phthalocyaninato)ytterbium(III)-Stearic Acid Langmuir- Blodgett Films Electrode Analytical Characterization by X-Ray Photoelectron Spectroscopy of Quaternary Chalcogenides for Cathodes in Lithium Cells Behaviour of the Adsorbed C1' Intermediate in Anodic C1 Evolution at Thin-film RuO Surfaces Electrode position Electrodeposition and Study of Multilayered Co/Cu Structures Electron diffraction Growth of II-VI Compounds by Metal-organic Chemical Vapour Deposition Electron microscopy Electron Microscopic Study of the Morphology of Lead Sulphide Growth Technique Electron paramagnetic resonance spectroscopy Electron Paramagnetic Resonance Spectroscopy of Cu+/Cu2 p"-Alumina Characterization of Epitaxially Grown ZnS Mn Films on a GaAs(100) Substrate prepared by the Hot-wall Epitaxy Technique Nature of Dangling-bond Sites in Native Plasma-polymerized Films of Unsaturated Hydrocarbons and Electron Paramagnetic Resonance Kinetics on Heat Treatment of the Films Electron-beam resist Radiation Chemical Yields and Lithographic Performance of Electron-beam Resists based on Poly(methy1styrene-co- Variation with Composition of the Intrinsic Sensitivity of Halogen-substituted Styrene Copolymers to Electron-beam Radiation Electron-transfer salt Novel Co-operative Magnetic Properties of Decamethylmanganocenium 2,3-Dichloro-5,6- Electroreductive polymerisation Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5-pyridine) Encapsulation Effective Method for Encapsulation of Titanium Dioxide and Enzyme immobilization Matrix Surface Modification by Plasma Polymerization for Enzyme Immobilization High-surface-area Resins derived from 2,3-Epoxypropyl Methacrylate cross-linked with Trimethylolpropane Trimethacrylate 371.Etruria Marl Time-resolved Powder Neutron Diffraction Study of Thermal Reactions in Clay Minerals Exfoliation Chemical Reduction of FeC1,-Graphite Intercalation Compounds with Potassium-Naphthalene Complex in Tetrahydrofuran Faujasite Dealumination of Hexagonal Polytype of Faujasite by Treatments with Silicon Tetrachloride Vapour Feature article Materials Chemistry An Overview Solid Electrolytes and Mixed Ionic-Electronic Conductors An Applications Overview Chirality in Liquid Crystals Photoemission in the Study of Oxide Superconductors Charge Fluctuations and an Ionic-Covalent Transition in La -. Sr,CuO Optical Properties of Sol-Gel Glasses doped with Organic Molecules Ferrocene Electrochemical Probing of the Sol-Gel-Xerogel Evolution Ferroelectricit y Chirality in Liquid Crystals Correlation between Absolute Configuration of Benzylic Chiral Centre and Sign of Spontaneous Polarization of Chiral Dopants for Ferroelectric Liquid Crystals Ferromagnet a Curie Temperature of K I5 Ferromagnetic coupling Novel Co-operative Magnetic Properties of Decamethylmanganocenium 2,3-Dichloro-5,6- dicyanobenzoquinoneide [Mn(C Me,),]' [DDQ] .-,479 Fibre. Preparation of Submicrometre Spherical Oxide Powders and Fibres by Thermal Spray Decomposition using an Ultrasonic Mist Atomiser Flash calcine Evolution of Structural Changes during Flash Calcination of Kaolinite Flash Calcination of Kaolinite Mechanistic Information from Thermogravimetry Fluorinated alkene Effective Method for Encapsulation of Titanium Dioxide and Fractal Role of Fractal Structure on Thin-film Processing of YBa,Cu,O -x using Alkoxide Sols Friedel-Crafts Aromatic Ether-Ketone-‘X’ Polymers Aromatic Ether-Ketone-‘X’ Polymers Part 2.-EK-Imide Copolymers Functionalised network Simple and Convenient Method for Preparing Functionalised Network Organopolysilanes Functionalized polyester Mesomorphic Behaviour of some Cross-linked Derivatives of All- Gallium arsenide Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si(lOO) Gallium borate Luminescence Spectra of Pure and Doped GaBO and LiGaO Gallium(II1) Luminescence Spectra of Pure and Doped GaBO and LiGaO Gamma-ray-induced polymerisation Effective Method for Encapsulation of Titanium Dioxide and Gas sensor Dopant Effects on the Response of Gas-sensitive Resistors Utilising Semiconducting Oxides Gibbsite Thermal Transformation Sequences of Alumina Hydrates.Part Glass-transition temperature Synthesis and Characterization of Isomeric Biphenyl-containing Poly(ary1 ether-bisketone)s. Part 1. -Polymers derived from Glassy carbon. Surface Structure of a Glassy Carbon GI ycolipid Preparation of Ternary Composite Hydrogels of Agarose Concanavalin A and a Glycolipid Monolayer and their Permeation Properties Grain boundary phase Preparation and Crystal Structure of U-Phase Ln,(Si3 xA13+x)Olz+xN2 xLn=La Nd) Graphite Chemical Reduction of FeC1,-Graphite Intercalation Compounds with Potassium-Naphthalene Complex in Tetrahydrofuran Hafnia Preparation of Uniform Colloidal Particles of Hafnium Compounds Hafnium hydroxysulphate Preparation of Uniform Colloidal Particles of Hafnium Compounds Halogenated polystyrene Variation with Composition of the Intrinsic Sensitivity of Halogen-substituted Styrene Copolymers to Electron-beam Radiation Helicity Chirality in Liquid Crystals Semi-crystalline Alkali-metal Salt Complexes with Poly(oligooxyethyleneoxy-1,2-phenylene)s,507 Hexa(4-alkylphenoxymethy1)benzeneColumnar Mesophases of Cyclic Trimers of Disubstituted Acetylenes Hexagonal tungsten trioxide framework Ammonium-ion Motions in the Hexagonal Tungsten Trioxide Framework H30+ Reorientation Reorientational Motions of Hydrogenic Species in 12- Tungstophosphoric Acid 14-Hydrate A Neutron Scattering Study High pressure Pressure-sensitive Absorption Spectra of Thin Films of Bis(diphenylglyoximato)platinum(II) Pt(dpg), Potential Application as an Indicator of Pressure High-resolution transmission electron microscopy Growth of ‘124‘ and ‘247’ Phases studied by High-resolution Transmission Electron Microscopy in HoBa,Cu,O -Ceramics prepared under Normal Oxygen Pressure Hole drift mobility Arylaldehyde and Arylketone Hydrazones as a New Class of Amorphous Molecular Materials Hole location Madelung Energy and Hole Location in YBa,Cu408 Hole pairing Elastic and Coulombic Contributions to Real-space Hole Pairing Hot-wall epitaxy Characterization of Epitaxially Grown ZnS :Mn Films on a GaAs( 100) Substrate prepared by the Hot-wall Epitaxy Technique Hydrogen molybdenum bronze Reorientation of Mo-co-ordinated Water Molecules in High- H ydrosilation Photoinduced Reversible Refractive-index Changes in Tailored Siloxane-based Polymers Hydrothermal synthesis Structural Phase Transition of VO,(B) to VO,(A) H ydrox ypolyester Dielectric Relaxation in Hydroxypolyesters Hysteresis A New Insulating Ferromagnet with Image reversal.Photogenerated Amines and their Use in the Design of a Positive-tone Resist Material based on Electrophilic Aromatic Substitution Incoherent inelastic neutron scattering Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Incommensurate structure Characterization of Ca-doped Biz +xSr2 -,CuO Indium Synthesis and Crystal Structures of the Layered I-111-V Zintl Phases K4In where X=As Sb Infrared reflection spectroscopy Infrared Reflectance Spectra of Sb-doped SnO Ceramics Infrared spectroscopy Generation of Charge Carriers and an H/D Isotope Effect in Proton-conducting Doped Barium Cerate Ceramics Docosanoyl Itaconate/ 1-Docosylamine Alternate-layer Langmuir- Blodgett Films Polymerisation Pyroelectric Properties and Infrared Spectroscopic Studies Insulator a Curie Temperature of 5I K Interatomic potential Calculation of Structural and Defect Properties of a-U308 Computer-simulation Study of Alkali-metal Insertion into Intercalation Mechanism of n-Alkylammonium Ion Intercalation into the Layered Host a-VOP04.2H20 . Single-crystal Conductivity Study of the Tin Dichalcogenides SnS2 -$ex Intercalated with Cobaltocene Intercalation of 2-Aminoethylferrocene into the Layered Host Lattices MOO 2H-TaS2 and a-Zr(HPO,),. H,O High-resolution Solid-state 13P and Il9Sn Magic-angle Spinning Nuclear Magnetic Resonance Studies of Amorphous and Microcrystalline Layered Metal(1v) Hydrogenphosphates Computer-simulation Study of Alkali-metal Insertion into Tetrathiafulvalene-FePS Layered Intercalation Compound A New Type of Organic-Inorganic Metal Preparation of Novel Intercalation Compounds of Silver and Copper in Layered Perovskites ALaNb20 Chemical Intercalation of Magnesium into Solid Hosts Chemical Reduction of FeC1,-Graphite Intercalation Compounds with Potassium-Naphthalene Complex in Tetrahydrofuran Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Intermolecular interaction Database Analysis of Crystal-structure-determining Interactions Metals Crystal Structures of Chiral Smectogenic 4'-0ctylbiphenyl-4-y1 p- Methylheptyloxy]biphenyl-4-carboxylate,667 Intrinsic viscosity Synthesis Characterization and Biodegradation Test of Nylon Iodometry Improved Method for the Determination of the Oxygen Content Ion exchange Spectroscopy A Powerful Probe for the Study of Lithium- Sol-Gel Synthesis of Zr(HPO,),-H,O Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Ionic conductivity Synthesis Structure and Ionic Conductivity in Nitrite Sodalites Liquid-like Lithium Ion Conductivity in Li -,,Al,GeO Solid Electrolyte Synthesis of a Crowned Azobenzene Liquid Crystal and its Application to Thermoresponsive Ion-conducting Films Generation of Charge Carriers and an HID Isotope Effect in Proton-conducting Doped Barium Cerate Ceramics Correlation of Surface Acidity with Electrical Conductivity of Silica-supported Heteropoly Compounds studied by the Complex-impedance Method Ionic-electronic conductor Solid Electrolytes and Mixed Ionic-Electronic Conductors An Applications Overview Iridium Synthesis and Mesomorphism of Stilbazole Complexes of Rhodium(1) and Iridium(I) Low-temperature Vapour Deposition of High-purity Iridium Coatings from Cyclooctadiene Complexes of Iridium Iridium dioxide Depth Profiles and Electrochemical Properties of IrO Electrocatalysts Stabilized with TiO X-Ray Diffraction Characterization of Iridium Dioxide Electrocatalysts 51I Iron phosphate X-Ray Photoelectron and Mossbauer Spectroscopies of a Binary Iron Phosphate Glass Iron(1Ir) chloride Chemical Reduction of FeC1,-Graphite Intercalation Compounds with Potassium-Naphthalene Complex in Tetrahydrofuran Kaolinite Evolution of Structural Changes during Flash Calcination of Kaolinite Flash Calcination of Kaolinite Mechanistic Information from Thermogravimetry Time-resolved Powder Neutron Diffraction Study of Thermal Reactions in Clay Minerals Langmuir monolayer Oriented Nucleation of CaCO from Metastable Solutions under Langmuir Monolayers Langmuir-Blodgett film Spectroscopic and X-Ray Diffraction Study of Langmuir-Blodgett Films of some 1,4,8,11,15,18-Hexaalkyl-22,25-Preparation of Ternary Composite Hydrogels of Agarose Concanavalin A and a Glycolipid Monolayer and their Permeation Properties. Formation of Ordered Multilayers by Stepwise Oligomerisation Docosanoyl Itaconate/ 1-Docosylamine Alternate-layer Langmuir- Blodgett Films Polymerisation Pyroelectric Properties and Infrared Spectroscopic Studies Electrochemical Salt Formation in Bis(phthalocyaninato)ytterbium(III)-Stearic Acid Langmuir- Blodgett Films Lanthanum niobium oxide Preparation of Novel Intercalation Compounds of Silver and Copper in Layered Perovskites ALaNb,O Lanthanum-strontium-copper-oxygen system Structure of La Sr ,CuO,.La -,Sr,CuO -6 Structural Magnetic and Transport Measurements on Antiferromagnets Insulators and Superconductors Laponite Spectroscopy A Powerful Probe for the Study of Lithium- Latex Zirconium Compounds as Coatings on Polystyrene Latex and as Hollow Spheres Lattice-energy minimisation Defect Calculations in Solids beyond the Dilute Limit Layered material Tetrathiafulvalene-FePS Layered Intercalation Compound A New Type of Organic-Inorganic Metal Synthesis and Crystal Structures of the Layered I-111-V Zintl Phases K,In,X6 where X =As Sb 555. Lead sulphide Electron Microscopic Study of the Morphology of Lead Sulphide Growth Technique Lead titanate Diol-based Sol-Gel System for the Production of Thin Films of PbTiO Li,O-(Nb,O Ta,O,)-ZrO system New Perovskite Phases in the Systems Li,O-(Nb,O,,Ta,O,)- ZrO Line broadening X-Ray Diffraction Characterization of Iridium Dioxide Electrocatalysts Liquid crystal Mesogen exhibiting a Ch-A*-A Phase Sequence a Liquid- Di(arylethynyl)bis(trimethylphosphine)platinum(II) A New Series Thermal and X-Ray Diffraction Studies of Liquid Crystals Paramagnetic Rod-like Liquid Crystals Bis[5-(4- Alkyloxy-substituted CTTV Derivatives that exhibit Columnar Mesophases Synthesis and Mesomorphism of Stilbazole Complexes of Rhodium(1) and Iridium(I) High-birefringence Materials using Metal-containing Liquid Crystals Synthesis of a Crowned Azobenzene Liquid Crystal and its Application to Thermoresponsive Ion-conducting Films Photoinduced Phase Transitions in Novel Liquid-crystalline Copolymers Chirality in Liquid Crystals Dielectric Relaxation Spectroscopy and Molecular Dynamics of a Liquid-crystalline Polyacrylate containing Spiropyran Groups Vitrification in Low-molecular-weight Mesogenic Compounds Crystal Structures of Chiral Smectogenic 4-Octylbiphenyl-4-yl p- Methylheptyloxy]biphenyl-4-carboxylate,667 Liquid-crystalline Zinc and Nickel 1,4,8,11,15,18,22,25- Octaalkylphthalocyaninates:Beneficial Effect of the Zinc Ion Correlation between Absolute Configuration of Benzylic Chiral Centre and Sign of Spontaneous Polarization of Chiral Dopants for Ferroelectric Liquid Crystals Synthesis and Thermal Behaviour of Mesomorphic Cu" Schiff's Base Complexes Columnar Mesophases of Cyclic Trimers of Disubstituted Acetylenes Preparation and Thermal Properties of New Liquid Crystals with Thermochromism and Solvatochromism of Bis[ 1,2-bis(3,4-di-n- Complexes Synthesis and Phase Behaviour of Mesomorphic Transition-metal Complexes of Alkoxydithiobenzoates Linear Dichroism of Mesomorphic Transition-metal Complexes Mesomorphic Behaviour of some Cross-linked Derivatives of All- Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Lithium Liquid-like Lithium Ion Conductivity in Li -,,A1,GeO4 Solid Electrolyte Lithium aluminogermanate Synthesis and Properties of a New Family of Phases Li,XYO, X=Al Ga; Y =Si Ge Lithium aluminosilicate Synthesis and Properties of a New Family of Phases Li,XYO, X =Al Ga; Y =Si Ge Lithium calcium phosphate Synthesis and Structure of LiCaPO by Combined X-Ray and Neutron Powder Diffraction Lithium cell Analytical Characterization by X-Ray Photoelectron Spectroscopy of Quaternary Chalcogenides for Cathodes in Lithium Cells Lithium gallium dioxide Luminescence Spectra of Pure and Doped GaBO and LiGaO Lithium ion conductor Crystal Chemistry of Lithium Gallium Silicate Li,- ,,Ga,SiO Solid Electrolytes Structure and Conductivity of an Li,SiO,-Li,SO Solid Solution Phase Lithium silicate.Structure and Conductivity of an Li4Si04-Li,S04 Solid Solution Phase Lithium sulphate Structure and Conductivity of an Li,SiO,-Li,SO Solid Solution Phase Lit hium-6 Spectroscopy A Powerful Probe for the Study of Lithium- Lithography Radiation Chemical Yields and Lithographic Performance of Electron-beam Resists based on Poly(methy1styrene-co- Variation with Composition of the Intrinsic Sensitivity of Halogen-substituted Styrene Copolymers to Electron-beam Radiation Living cationic polymerization Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization.Part 13. -Synthesis and Living Cationic Polymerization of (S)-(-)-2-Methylbutyl 4-(o-Vinyloxy)-Groups Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Low-temperature synthesis Low-temperature Synthesis of Perovskite Solids LaMO (M =Ni Co Mn) via Binuclear Complexes of Compartmental Ligand N,N’-Bis(3-carboxysalicylidene)ethylenediamine,78 Luminescence Luminescence Spectra of Pure and Doped GaBO and LiGaO Luminescent material Electron Paramagnetic Resonance Spectroscopy of Cu+/Cu2 p”-Alumina Luminescence Properties of A,ReCl Crystals Madelung potential Madelung Energy and Hole Location in YBa,Cu,O Magic-angle spinning nuclear magnetic resonance spectroscopy Isomorphous Substitution in Non-linear Optical KTiOPO Spectroscopy A Powerful Probe for the Study of Lithium- Evolution of Structural Changes during Flash Calcination of Kaolinite High-resolution Solid-state 13P and 19Sn Magic-angle Spinning Nuclear Magnetic Resonance Studies of Amorphous and Microcrystalline Layered Metal(1v) Hydrogenphosphates Magnesium Chemical Intercalation of Magnesium into Solid Hosts Magnesium oxide Magnesium Oxide as a Support Material for Dehydrogenation Catalysts Magnetic frustration Magnetic Frustration Spirals and Short-range Order in Cr,Fe _,VO4-I Solid Solutions Magnetism Synthesis and Characterisation of [(q-C,Me,)Ru(p,q-C,Me,)Ru(q-C,Me5)]+[A]-; [A]- =TCNE TCNQ C,[C(CN),] Magnetization Electrodeposition and Study of Multilayered Co/Cu Structures Manganese oxide Carbon Deposition on Iron-Manganese-Chromium Spinels Materials overview Materials Chemistry An Overview Mechanochemistry Structural Phase Transition of VO,(B) to VO,(A) Mesophase Preparation and Thermal Properties of New Liquid Crystals with Metal alkoxide precursor Low-temperature Synthesis of YBa,Cu,O Films by Solution Process using Y-Ba-Cu Heterometallic Alkoxide Metal dithiolene complex Crystal Structure and Pressure Dependence of Electrical Conductivities of [(CH,),N][Pt(drnit),] Metal-insulator transition La -,Sr,CuO -6 Structural Magnetic and Transport Measurements on Antiferromagnets Insulators and Superconductors Metallocene Synthesis and Characterisation of [(q-C,Me,)Ru(p,q-C,Me,)Ru(q-C,Me,)]+[A]-; [A]-=TCNE TCNQ C,[C(CN),]3 Metallomesogen Di(arylethynyl)bis(trimethylphosphine)platinum(rI) A New Series Paramagnetic Rod-like Liquid Crystals Bis[5-(4- Synthesis and Mesomorphism of Stilbazole Complexes of Rhodium(1) and Iridium(I) 251.High-birefringence Materials using Metal-containing Liquid Crystals Synthesis and Phase Behaviour of Mesomorphic Transition-metal Complexes of Alkoxydithiobenzoates Metal-organic chemical vapour deposition Chemical Vapour Deposition of Aluminium Silicate Thin Films Low-temperature Vapour Deposition of High-purity Iridium Coatings from Cyclooctadiene Complexes of Iridium Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si(lOO) Low-temperature Vapour Deposition of High-purity Copper Coatings from Bis[N-(Fluoroalkyl)salicylaldiminato]copper Chelates Growth of 11-VI Compounds by Metal-organic Chemical Vapour Deposition Metal(1v) hydrogenphosphate High-resolution Solid-state 13P and 19Sn Magic-angle Spinning Nuclear Magnetic Resonance Studies of Amorphous and Microcrystalline Layered Metal(1v) Hydrogenphosphates Metal-support interaction Promotion of the Metal-Oxide Support Interaction in the Ni/ Ti0 Catalyst Metal-to-non-metal transition Metal-to-non-metal Transitions in High-temperature Oxide Superconductors monitored by Photoelectron Spectroscopy.Microdomain Investigation of Defect Ordering in the Perovskite System Synthesis Structure and Electrical Properties of Sr,CuO,(CO,) an Oxide Carbonate related to Perovskite SrCro ,Fe0,,O3-y by Mossbauer Spectroscopy Microlithography Photogenerated Amines and their Use in the Design of a Positive-tone Resist Material based on Electrophilic Aromatic Magnetic Frustration Spirals and Short-range Order in Synthesis and Structure of LiCaPO by Combined X-Ray and Cr,Fe -.V04-I Solid Solutions Neutron Powder Diffraction Substitution Microwave heating 6Li Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy A Powerful Probe for the Study of Lithium- containing Materials Mixed oxide precursor Oxysalts Characterization Characterization of Copper-Manganese Hydroxysalts and Copper-Cobalt Hydroxysalts and Oxysalts Bulk and Surface Mixed valence Nickel complex Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5-pyridine) Nickel oxide Effect of Nickel Oxide on the Sintering Characteristics and Phase Stability of Zirconia-12 mol% Ceria Ceramics Niobium oxide Electrochromic Nb205 and Nb,O,/Silicone Composite Thin Films prepared by Sol-Gel Processing Ni/Ti02 catalyst Promotion of the Metal-Oxide Support Interaction in the Ni/ Mobility in clays Madelung Energy and Hole Location in YBa2Cu40s 6Li Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy A Powerful Probe for the Study of Lithium-containing Materials Modified electrode Microstructural Studies on Polypyrrole Scanning Tunnelling Microscopy Study of Osmium-containing Electroactive Metallopolymer [0 (bipy),(PVP) Cl]C1 Films on Polycrystalline Graphite Electrodes Effect of Composition of Polymer Backbone on Spectroscopic and Electrochemical Properties of Ruthenium(r1) Bis(2,2'- bipyridy1)-containing 4-Vinylpyridine/Styrene Copolymers Mossbauer spectroscopy Investigation of Defect Ordering in the Perovskite System SrCro,,Feo,,O -y by Mossbauer Spectroscopy Intercalation of 2-Aminoethylferrocene into the Layered Host Lattices MOO 2H-TaS and cr-Zr(HPO4),.H2O High-resolution Solid-state 13Pand "'Sn Magic-angle Spinning Nuclear Magnetic Resonance Studies of Amorphous and Microcrystalline Layered Metal(1v) Hydrogenphosphates X-Ray Photoelectron and Mossbauer Spectroscopies of a Binary Iron Phosphate Glass Molecular metal Tetrathiafulvalene-FePS Layered Intercalation Compound A New Type of Organic-Inorganic Metal Molecular sieve Synthesis and Crystal Structure of a Novel Beryllium Phosphate Open-framework Structure Molybdenum Novel Chemical Preparative Route for Semiconducting MoSe Thin Films Monodispersion Preparation of Uniform Colloidal Particles of Hafnium Compounds Monolayer Preparation of Ternary Composite Hydrogels of Agarose Concanavalin A and a Glycolipid Monolayer and their Permeation Properties Multila yer Formation of Ordered Multilayers by Stepwise Oligomerisation Electrodeposition and Study of Multilayered Co/Cu Structures TiO Catalyst p-Nitroaniline Second-harmonic Generation from Mixed Crystals of p-Nitroaniline with Substituted Benzenes studied by the Powder Method Nitrogen ceramic Preparation and Crystal Structure of U-Phase Ln,(Si -xA13 +JO +,N2- ( 0.5,Ln =La Nd) Non-aqueous dispersion polycondensation Non-linear optical material Preparation of Spherical Aromatic Polyimide Particulates Isomorphous Substitution in Non-linear Optical KTiOPO Non-linear Optical Properties of Group Metal Alkynyls and Isomorphous Substitution in Non-linear Optical KTiOPO Second-harmonic Generation Properties of some Co-ordination Compounds based on Pentanedionato Ligands Preparation and Second-harmonic Generation Properties of Tris(pyrocatecholato)stannate(Iv) Compounds Trivalent Boron as Acceptor Chromophore in Asymmetrically Substituted 4,4'-Biphenyl and Azobenzene for Non-linear Optics Studies of Non-linear Optical Organic Materials Crystal and Molecular Structure of 2-Dicyanomethylene-1,3-dioxolane their Polymers Nuclear magnetic resonance spectroscopy ,'A1 Nuclear Magnetic Resonance Spectroscopy Investigation of Thermal Transformation Sequences of Alumina Hydrates.Part 1. -Gibbsite y-Al(OH) Sol-Gel Synthesis of ZI-(HPO,) . H O Nuclear Magnetic Resonance Spectroscopy Investigation of Thermal Transformation Sequences of Alumina Hydrates Part 2.-Boehmite 6-A100H Nucleation Oriented Nucleation of CaCO from Metastable Solutions under Langmuir Monolayers Nucleophilic aromatic substitution Synthesis and Characterization of Isomeric Biphenyl-containing Poly(ary1 ether-bisketone)s. Part 1. -Polymers derived from 4,4-(p-Fluorobenzoy1)biphenyl and Bisphenols Nylon Synthesis Characterization and Biodegradation Test of Nylon and Nylon Nematic phase Synthesis and Thermal Behaviour of Mesomorphic Cu" Schiff's Base Complexes Neutron diffraction Synthesis and Structure of Ba,CaCu2,,,06,96(C03)0.5,a Perovskite containing Carbonate Anions and Related Phases KUO Ceramic Superconductors produced using Sol-Gel Techniques Powder Neutron Diffraction Study of Potassium Uranate(v) Structure Evolution during Thermal Processing of High-T Structure of Lao,,Sro ,Cu0,,6 Thermal Decomposition of Cobalt(I1) Acetate Tetrahydrate studied with Time-resolved Neutron Diffraction and Thermogravimetric Analysis I Oligomerisation Formation of Ordered Multilayers by Stepwise Oligomerisation OligothiopheneAlkyl-substituted Oligothiophenes Crystallographic and Spectroscopic Studies of Neutral and Doped Forms Olivine Formation of Q8M10{ [(CH,),SiO] loSi,Ol 1} from QM4{ [(CH,),SiO],Si} Olivine and Dioptase Optical absorption Synthesis and Optical Spectroscopy of Platinum-metal-containing Di- and Tri-acetylenic Polymers Optical activity Mesogen exhibiting a Ch-A*-A Phase Sequence a Liquid- Pressure-sensitive Absorption Spectra of Thin Films of crystalline Analogue of the Abrikosov Phase Bis(diphenylglyoximato)platinum(n) Pt(dpg), Potential Application as an Indicator of Pressure Optical communication Photoinduced Reversible Refractive-index Changes in Tailored Siloxane-based Polymers Optical data storage Photoinduced Phase Transitions in Novel Liquid-crystalline Copolymers Organic metal Database Analysis of Crystal-structure-determining Interactions Metals Organic molecule Optical Properties of Sol-Gel Glasses doped with Organic Molecules Organic semiconductor Phase Transition of Tetrakis(octy1thio)tetrathiafulvalene(TTC8-TTF) and Crystal Structure Analysis Oxonol Dyes X-Ray Crystallographic and Solid-state 13C Nuclear Magnetic Resonance Studies of some Organic Semiconductors Organic-inorganic composite Characterization of Conducting Polymer-Quartz Composites Organometallic complex Synthesis and Characterisation of [(q-C,Me,)Ru(p,q-C,Me,)Ru(q-C,Me,)]+[A]-; [A]- =TCNE TCNQ C3[C(CN),]3 Organosilicon polymer Simple and Convenient Method for Preparing Functionalised Network Organopolysilanes Oxidation Characterization of Copper-Manganese Hydroxysalts and Oxysalts Oxidative addition Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5-pyridine) Oxide carbonate Synthesis and Structure of Ba,CaCU,,,,O6,96(CO,) ,5 a Perovskite containing Carbonate Anions and Related Phases Oxide conductor Compound and Solid-solution Formation Phase Equilibria and Electrical Properties in the Ceramic System Zr0,-La,O,- Ta205 The Bi,O,-Sm,O System Phase Diagram and Electrical Properties Oxide superconductor Metal-to-non-metal Transitions in High-temperature Oxide Superconductors monitored by Photoelectron Spectroscopy Bi-Sr-Ca-Cu-0 High-T Superconductors produced by using a Rapid Thermal Melt Processing Technique Characterization of Ca-doped Biz +3r2 -,CuO Role of Fractal Structure on Thin-film Processing of YBa,Cu,O,- using Alkoxide Sols Elastic and Coulombic Contributions to Real-space Hole Pairing Photoemission in the Study of Oxide Superconductors Phase Relations in the System Bi0,,5-SrO-Cu0 at K Charge Fluctuations and an Ionic-Covalent Transition in La -,Sr,CuO Improved Method for the Determination of the Oxygen Content Growth of ‘124‘ and ‘247’ Phases studied by High-resolution Transmission Electron Microscopy in HoBa,Cu,O -Ceramics prepared under Normal Oxygen Pressure Low-temperature Synthesis of YBa,Cu,O -x Films by Solution Process using Y-Ba-Cu Heterometallic Alkoxide Oxonol dye Oxonol Dyes X-Ray Crystallographic and Solid-state 13C Nuclear Magnetic Resonance Studies of some Organic Semiconductors Paramagnetism Paramagnetic Rod-like Liquid Crystals Bis[5-(4- Perfluoralkyl compound Thermal and X-Ray Diffraction Studies of Liquid Crystals Permeation Preparation of Ternary Composite Hydrogels of Agarose Concanavalin A and a Glycolipid Monolayer and their Permeation Properties Perovskite Synthesis and Structure of Ba,CaCU,,,,O6,96(C03)0,5,a Perovskite containing Carbonate Anions and Related Phases Investigation of Defect Ordering in the Perovskite System SrCr,,,Fe,,,O -y by Mossbauer Spectroscopy Generation of Charge Carriers and an H/D Isotope Effect in Proton-conducting Doped Barium Cerate Ceramics Preparation of Novel Intercalation Compounds of Silver and Copper in Layered Perovskites ALaNb,O Synthesis Structure and Electrical Properties of Sr,Cu02(C03) New Perovskite Phases in the Systems Li,0-(Nb20,,Ta205)- ZrO Low-temperature Synthesis of Perovskite Solids LaMO (M = Ni Co Mn) via Binuclear Complexes of Compartmental Ligand N,N’-Bis(3-carboxysalicylidene)ethylenediamine,78 Optical Properties of Sol-Gel Glasses doped with Organic Molecules Growth of ‘124‘ and ‘247’ Phases studied by High-resolution Transmission Electron Microscopy in HoBa,Cu,O -x Ceramics prepared under Normal Oxygen Pressure Growth of ‘124‘ and ‘247’ Phases studied by High-resolution Transmission Electron Microscopy in HoBa,Cu,O - Ceramics prepared under Normal Oxygen Pressure Growth of ‘124’ and ‘247’ Phases studied by High-resolution Transmission Electron Microscopy in HoBa,Cu,O -Ceramics prepared under Normal Oxygen Pressure Phase equilibria Phase Relations in the System BiO,,,-SrO-CuO at K Phase retention Effect of Nickel Oxide on the Sintering Characteristics and Phase Stability of Zirconia- mol% Ceria Ceramics Phase transition Mesogen exhibiting a Ch-A*-A Phase Sequence a Liquid- Phase Transition of Tetrakis(octy1thio)tetrathiafulvalene (TTC8-TTF) and Crystal Structure Analysis Photoinduced Phase Transitions in Novel Liquid-crystalline Copolymers Structural Phase Transition of VO,(B) to VO,(A) Phosphate Isomorphous Substitution in Non-linear Optical KTiOPO Sol-Gel Synthesis of Zr(HPO,),.H,O Crosslinked Layered Materials formed by Intercalation of Octameric Siloxanes in Metal(rv) Hydrogen Phosphates Photoactive polymer Photoinduced Phase Transitions in Novel Liquid-crystalline Copolymers Photoinduced Reversible Refractive-index Changes in Tailored Siloxane-based Polymers Photochromism.Dielectric Relaxation Spectroscopy and Molecular Dynamics of a Liquid-crystalline Polyacrylate containing Spiropyran Groups Photoemission Metal-to-non-metal Transitions in High-temperature Oxide Superconductors monitored by Photoelectron Spectroscopy Photoemission in the Study of Oxide Superconductors Surface Segregation of Sr in Doped MgO X-Ray Photoelectron and Mossbauer Spectroscopies of a Binary Iron Phosphate Glass Photogenerated base Photogenerated Amines and their Use in the Design of a Positive-tone Resist Material based on Electrophilic Aromatic Substitution Photoisomerisat ion Photoinduced Phase Transitions in Novel Liquid-crystalline Copolymers.Photoluminescence Synthesis and Optical Spectroscopy of Platinum-metal-containing Di- and Tri-acetylenic Polymers Photoluminescence spectroscopy Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si(lOO) 663Phthaloc yanine Spectroscopic and X-Ray Diffraction Study of Langmuir- Blodgett Films of some 1,4,8,11,15,18-Hexaalkyl-22,25-Liquid-crystalline Zinc and Nickel 1,4,8,11,15,18,22,25- Octaalkylphthalocyaninates Beneficial Effect of the Zinc Ion Electrochromism in Titanyl and Vanadyl Phthalocyanine Thin Films Pillaring Porous Cross-linked Materials formed by Oligomeric Aluminium Hydroxides and a-Tin Phosphate Porous Chromia-pillared a-Zirconium Phosphate Materials Crosslinked Layered Materials formed by Intercalation of Octameric Siloxanes in Metal(1v) Hydrogen Phosphates Plasma polymerization Nature of Dangling-bond Sites in Native Plasma-polymerized Films of Unsaturated Hydrocarbons and Electron Paramagnetic Resonance Kinetics on Heat Treatment of the Films Matrix Surface Modification by Plasma Polymerization for Enzyme Immobilization Platinum acetylide Di(arylethynyl)bis(trimethylphosphine)platinum( )A New Series Polarizabilit y Dielectric Relaxation in Hydroxypolyesters Dielectric Relaxation Peaks in the Low-frequency/High- the Thermostimulated Depolarization Current (TSDC) Technique in 2,3,7,8-Tetramethoxychalcogenanthrenes-TCNQ Charge-transfer Complexes Polaron Elastic and Coulombic Contributions to Real-space Hole Pairing Poly(2,5pyridine) Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5-pyridine) Polyamide Preparation and Characterization of wholly Aromatic para-Linked Copolyamides of Poly(p-phenyleneterephthalamide) Pol yaniline Novel conducting Soluble Co-polymers of Aniline X-Ray Photoelectron Spectroscopy of New Soluble Polyaniline Perchlorates Evidence for the Coexistence of Polarons and Bipolarons Polyether-alkali-metal salt complex Semi-crystalline Alkali-metal Salt Complexes with Poly(o1igooxyet hyleneoxy- 1,2-phenylene)s Poly(ether-ketone) Aromatic Ether-Ketone-'X Polymers Aromatic Ether-Ketone-'X' Polymers Part 2.-EK-Imide Copolymers Polyimide Aromatic Ether-Ketone-'X Polymers Part 2.-EK-Imide Copolymers Polymer backbone Effect of Composition of Polymer Backbone on Spectroscopic bipyridy1)-containing 4-Vinylpyridine/Styrene Copolymers Poly(meth ylst yrene-co-chlorostyrene) Radiation Chemical Yields and Lithographic Performance of Electron-beam Resists based on Poly(methy1styrene-co- Pol ymorph Thermal Decomposition of Cobalt(i1) Acetate Tetrahydrate Thermogravimetric Analysis Polypeptide Synthesis and Conformational Study of Cuticle Collagen Models Polypyrrole Characterization of Conducting Polymer-Quartz Composites Polyyne polymers Synthesis and Optical Spectroscopy of Platinum-metal-containing Di- and Tri-acetylenic Polymers Porosity Porous Chromia-pillared a-Zirconium Phosphate Materials Potassium uranate(v) Powder Neutron Diffraction Study of Potassium Uranate(v) KUO Powder Preparation of Submicrometre Spherical Oxide Powders and Fibres by Thermal Spray Decomposition using an Ultrasonic Mist Atomiser Powder diffraction Isomorphous Substitution in Non-linear Optical KTiOPO Powder Neutron Diffraction Study of Potassium Uranate(v) KUO Structure of Lao,8Sro,2Cu02,64 Isomorphous Substitution in Non-linear Optical KTiOPO.Transformation of Schoepite into Uranyl Oxide Hydrates of the Bivalent Cations Mg2+ Mn2+ and Ni2+ Synthesis Structure and Electrical Properties of Sr,CuO,(CO,) Magnetic Frustration Spirals and Short-range Order in Cr,Fe -,V04-I Solid Solutions Synthesis and Structure of LiCaPO by Combined X-Ray and Neutron Powder Diffraction Pseudoboehmi te Thermal Transformation Sequences of Alumina Hydrates Part Pyroelectricity Docosanoyl Itaconate/l-DocosylamineAlternate-layer Langmuir- Blodgett Films Polymerisation Pyroelectric Properties and Infrared Spectroscopic Studies Quasielastic neutron scattering Ammonium-ion Motions in the Hexagonal Tungsten Trioxide Framework Reorientation of Mo-co-ordinated Water Molecules in High- Reorientational Motions of Hydrogenic Species in 12- Tungstophosphoric Acid 14-Hydrate A Neutron Scattering Study Radiolabelled enzyme Matrix Surface Modification by Plasma Polymerization for Enzyme Immobilization Radiotracer Alkali-metal Fluorides supported on y-Alumina Rapid thermal melt processing Bi-Sr-Ca-Cu-0 High-T Superconductors produced by using a Rapid Thermal Melt Processing Technique Rare-earth oxide Progress towards Preparation of High-surface-area Rare-earth Oxides Reduction Chemical Reduction of FeC1,-Graphite Intercalation Compounds with Potassium-Naphthalene Complex in Tetrahydrofuran Reentrant nematic mesophase Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Refractive index Photoinduced Reversible Refractive-index Changes in Tailored Siloxane-based Polymers Reorientation Reorientation of Mo-co-ordinated Water Molecules in High- Resist Photogenerated Amines and their Use in the Design of a Positive-tone Resist Material based on Electrophilic Aromatic Substitution Resistivity jump.Phase Transition of Tetrakis(octy1thio)tetrathiafulvalene (TTCB-TTF) and Crystal Structure Analysis Rhodium Synthesis and Mesomorphism of Stilbazole Complexes of Rhodium(1) and Iridium(i) Rietveld analysis Crystal Chemistry of Lithium Gallium Silicate Li,- ,,Ga,SiO Solid Electrolytes Isomorphous Substitution in Non-linear Optical KTiOPO Preparation and Crystal Structure of U-Phase Ln3(Si3-xA13+x)O12 xN2-xIsomorphous Substitution in Non-linear Optical KTiOPO Magnetic Frustration Spirals and Short-range Order in Cr,Fe -,VO,-I Solid Solutions Ruthenium Effect of Composition of Polymer Backbone on Spectroscopic bipyridy1)-containing 4-Vinylpyridine/Styrene Copolymers Ruthenium dioxide Behaviour of the Adsorbed C1' Intermediate in Anodic C1 Evolution at Thin-film RuO Surfaces Rutile New Antimoniate-Vanadate with the Rutile Structure Scanning electron microscopy Carbon Deposition on Iron-Manganese-Chromium Spinels Scanning tunnelling microscopy Surface Structure of a Glassy Carbon Microstructural Studies on Polypyrrole Scanning Tunnelling Microscopy Study of Osmium-containing Electroactive Me tallopol ymer [Os(bipy),( PVP) oCl] C1 Films Schiff's base Synthesis and Thermal Behaviour of Mesomorphic Cu" Schiff's Base Complexes Schoepite Transformation of Schoepite into Uranyl Oxide Hydrates of the Bivalent Cations Mg2+ Mn2+ and Ni2+ Scholl reaction Synthesis of Aromatic Polyethers by the Scholl Reaction Screw dislocation Mesogen exhibiting a Ch-A*-A Phase Sequence a Liquid- Secondary-ion mass spectrometry Secondary-ion Mass Spectrometry of the Superconducting Bi- Pb-Sr-Ca-Cu-0 System Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si( loo) Second-harmonic generation Second-harmonic Generation Properties of some Co-ordination Compounds based on Pentanedionato Ligands Second-harmonic Generation from Mixed Crystals of p-Nitroaniline with Substituted Benzenes studied by the Powder Method Preparation and Second-harmonic Generation Properties of Tris(pyrocatecholato)stannate(Iv) Compounds Studies of Non-linear Optical Organic Materials Crystal and Molecular Structure of 2-Dicyanomethylene- 1,3-dioxolane Sedimentation density Dispersion of Silicon Carbide Whiskers and Powders in Aqueous Selenium Novel Chemical Preparative Route for Semiconducting MoSe Thin Films Self-diffusion Reorientation of Mo-co-ordinated Water Molecules in High- Semiconductivity X-Ray Photoelectron and Mossbauer Spectroscopies of a Binary Iron Phosphate Glass Dopant Effects on the Response of Gas-sensitive Resistors Utilising Semiconducting Oxides Seven-membered ring system Preparation and Thermal Properties of New Liquid Crystals with Sialon material Preparation and Crystal Structure of U-Phase Ln,(Si -xA13+,)012Sigmatropy Preparation and Thermal Properties of New Liquid Crystals with ...XI11 Silicate organosiloxane hybrid Formation of QsMlo{[(CH3)3SiO]loSis ll QM4{ [(CH,),SiO],Si} Olivine and Dioptase Silicon carbide Dispersion of Silicon Carbide Whiskers and Powders in Aqueous Siloxane Crosslinked Layered Materials formed by Intercalation of Octameric Siloxanes in Metal(1v) Hydrogen Phosphates Silver ion exchange Synthesis Structure and Ionic Conductivity in Nitrite Sodalites Silver sulphide Electron Microscopic Study of the Morphology of Lead Sulphide Growth Technique Sintering Effect of Nickel Oxide on the Sintering Characteristics and Phase Stability of Zirconia-12 mol% Ceria Ceramics Smectic phase Thermal and X-Ray Diffraction Studies of Liquid Crystals Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization.Part 13.-Synthesis and Living Cationic Polymerization of (S)-(-)-2-MethylbutyI 4-(o-Vinyloxy)-Groups Crystal Structures of Chiral Smectogenic 4'-Octylbiphenyl-4-y1 p-Methylheptyloxy]biphenyl-4-carboxylate,667 Synthesis and Thermal Behaviour of Mesomorphic Cu" Schiff's Base Complexes Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization I0 Sodalite Synthesis Structure and Ionic Conductivity in Nitrite Sodalites Sol-gel processing Structure Evolution during Thermal Processing of High-T Ceramic Superconductors produced using Sol-Gel Techniques . Role of Fractal Structure on Thin-film Processing of YBa,Cu,O,- using Alkoxide Sols Electrochromic Nb,O and Nb,O,/Silicone Composite Thin Films prepared by Sol-Gel Processing Sol-Gel Synthesis of WO Thin Films Sol-Gel Synthesis of Zr(HPO,),.H,O Electrochemical Probing of the Sol-Gel-Xerogel Evolution Diol-based Sol-Gel System for the Production of Thin Films of PbTiO Optical Properties of Sol-Gel Glasses doped with Organic Molecules Solid electrolyte Solid Electrolytes and Mixed Ionic-Electronic Conductors An Applications Overview The Bi,O,-Sm,O System Phase Diagram and Electrical Properties Structure and Conductivity of an Li,Si04-Li,SO Solid Solution Phase Synthesis and Structure of LiCaPO by Combined X-Ray and Neutron Powder Diffraction Solid solution Liquid-like Lithium Ion Conductivity in Li -,,AI,GeO Solid Electrolyte Solid-state nuclear magnetic resonance spectroscopy Dealumination of Hexagonal Polytype of Faujasite by Treatments with Silicon Tetrachloride Vapour Intercalation of 2-Aminoethylferrocene into the Layered Host Lattices MOO 2H-TaS2 and a-Zr(HPO,),-H,O Oxonol Dyes X-Ray Crystallographic and Solid-state I3C Nuclear Magnetic Resonance Studies of some Organic Semiconductors Solid-state polymerisation Docosanoyl Itaconate/l-DocosylamineAlternate-layer Langmuir- Blodgett Films Polymerisation Pyroelectric Properties and Infrared Spectroscopic Studies Solvatochromism Thermochromism and Solvatochromism of Bis[ 1,2-bis(3,4-di-n- Trivalent Boron as Acceptor Chromophore in Asymmetrically Substituted 4,4'-Biphenyl and Azobenzene for Non-linear Optics Spherical polyimide particle Preparation of Spherical Aromatic Polyimide Particulates Spinel Solid-solution Formation Electrical Properties and Zero- Spray decomposition Preparation of Submicrometre Spherical Oxide Powders and Fibres by Thermal Spray Decomposition using an Ultrasonic Mist Atomiser Stearic acid Electrochemical Salt Formation in Bis(phthalocyaninato)ytterbium(m)-Stearic Acid Langmuir- Blodgett Films Steric stabilisation Preparation of Spherical Aromatic Polyimide Particulates Stoichiometry New Perovskite Phases in the Systems Li,0-(Nb,05,Ta,0,)- ZrO Improved Method for the Determination of the Oxygen Content.Strontium copper oxide carbonate Synthesis Structure and Electrical Properties of Sr,CuO,(CO,) Substituted benzene Second-harmonic Generation from Mixed Crystals of p-Nitroaniline with Substituted Benzenes studied by the Powder Method Sulphur Database Analysis of Crystal-structure-determining Interactions Metals Superconductivity Single-crystal Conductivity Study of the Tin Dichalcogenides SnS -,Sex Intercalated with Cobaltocene Secondary-ion Mass Spectrometry of the Superconducting Bi- Pb-Sr-Ca-Cu-0 System Structure Evolution during Thermal Processing of High-T Ceramic Superconductors produced using Sol-Gel Techniques Solid-solution Formation Electrical Properties and Zero- Room-temperature Electrochemical Reduction of YBa,Cu,O - La -,Sr,CuO Structural Magnetic and Transport Measurements on Antiferromagnets Insulators and Superconductors Charge Fluctuations and ar.Ionic-Covalent Transition in La -,Sr,CuO Supported heteropoly compound Correlation of Surface Acidity with Electrical Conductivity of Silica-supported Heteropoly Compounds studied by the Complex-impedance Method Surface area High-surface-area Resins derived from 2,3-Epoxypropyl Methacrylate cross-linked with Trimethylolpropane Trimethacrylate Surface modification Matrix Surface Modification by Plasma Polymerization for Enzyme Immobilization Surface polymerisation Effective Method for Encapsulation of Titanium Dioxide and Surface roughness Microstructural Studies on Polypyrrole Surface segregation Surface Segregation of Sr in Doped MgO Surface species Alkali-metal Fluorides supported on y-Alumina Surface structure Surface Structure of a Glassy Carbon Temperature-programmed desorption Dealumination of Hexagonal Polytype of Faujasite by Treatments with Silicon Tetrachloride Vapour Ternary Fluoride.Atomistic Lattice Simulations of the Ternary Fluorides AMF Tetragonal-packed structure Crystal Chemistry of Lithium Gallium Silicate Li -,,Ga,SiO Solid Electrolytes Tetramethylammonium ion Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Tetrathiafulvalene Phase Transition of Tetrakis(octy1thio)tetrathiafulvalene(TTC,-TTF) and Crystal Structure Analysis Thermal stability Thermal and Electrical Conduction Studies on Polypyrrole Tetracyanoplatinate Thermochromism Thermochromism and Solvatochromism of Bis[ 1,2-bis(3,4-di-n- Thermogravimetric analysis Generation of Charge Carriers and an H/D Isotope Effect in Proton-conducting Doped Barium Cerate Ceramics Thermal Decomposition of Cobalt(I1) Acetate Tetrahydrate Thermogravimetric Analysis.Flash Calcination of Kaolinite Mechanistic Information from Thermogravimetry Thermoresponse Synthesis of a Crowned Azobenzene Liquid Crystal and its Application to Thermoresponsive Ion-conducting Films Thermostimulated depolarization current Dielectric Relaxation Peaks in the Low-frequency/High- the Thermostimulated Depolarization Current (TSDC) Technique in 2,3,7,8-Tetramethoxychalcogenanthrenes-TCNQ Charge-transfer Complexes Thin film Chemical Vapour Deposition of Aluminium Silicate Thin Films Role of Fractal Structure on Thin-film Processing of YBa,Cu,O,- using Alkoxide Sols Novel Chemical Preparative Route for Semiconducting MoSe Thin Films Characterization of Epitaxially Grown ZnS Mn Films on a GaAs(100) Substrate prepared by the Hot-wall Epitaxy Technique Electrochromic Nb205 and Nb,O,/Silicone Composite Thin Films prepared by Sol-Gel Processing Low-temperature Vapour Deposition of High-purity Iridium Coatings from Cyclooctadiene Complexes of Iridium Sol-Gel Synthesis of WO Thin Films Behaviour of the Adsorbed C1' Intermediate in Anodic C1 Evolution at Thin-film RuO Surfaces Diol-based Sol-Gel System for the Production of Thin Films of PbTiO Characterization and Photoelectrochemical Studies of CuInS Thin Films Prepared by Sulphurization of Cu-In Alloy Pressure-sensitive Absorption Spectra of Thin Films of Bis(diphenylglyoximato)platinum(II) Pt(dpg), Potential Application as an Indicator of Pressure Time-of-flight neutron diffraction Isomorphous Substitution in Non-linear Optical KTiOPO Time-resolved powder neutron diffraction Time-resolved Powder Neutron Diffraction Study of Thermal Reactions in Clay Minerals Porous Cross-linked Materials formed by Oligomeric Aluminium Hydroxides and a-Tin Phosphate Titanate Solid-solution Formation Electrical Properties and Zero- Titanium dioxide Effective Method for Encapsulation of Titanium Dioxide and Depth Profiles and Electrochemical Properties of IrO Electrocatalysts Stabilized with TiO Titanium disulphide Chemical Intercalation of Magnesium into Solid Hosts TopographySurface Structure of a Glassy Carbon Scanning Tunnelling Microscopy Study of Osmium-containing Electroactive Metallopolymer [Os(bipy),(PVP),,C1]Cl Films Transition-metal complex Non-linear Optical Properties of Group Metal Alkynyls and Transition-metal spinel oxide Carbon Deposition on Iron-Manganese-Chromium Spinels Transmission electron microscopy Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si( loo) Alkali-metal Fluorides supported on ?-Alumina Triazine X-Ray Crystal Structure of a Triazine Adduct of Dimethylzinc An Important Precursor for the Deposition of II/VI Materials Tris(pyrocatecholato)stannate(Iv)compound Preparation and Second-harmonic Generation Properties of Tris(pyrocatecholato)stannate(Iv) Compounds Tungsten chloroalkoxide Sol-Gel Synthesis of WO Thin Films Reorientational Motions of Hydrogenic Species in 12- Tungstophosphoric Acid 14-Hydrate A Neutron Scattering Study Ultrasonic atomisation Preparation of Submicrometre Spherical Oxide Powders and Fibres by Thermal Spray Decomposition using an Ultrasonic Mist Atomiser Uranium oxide Calculation of Structural and Defect Properties of a-U308 Computer-simulation Study of Alkali-metal Insertion into Uranyl oxide hydrate Transformation of Schoepite into Uranyl Oxide Hydrates of the Bivalent Cations Mg2+ Mn2+ and Ni2+ Valence fluctuation Madelung Energy and Hole Location in YBa2Cu,08 Vanadate. New Antimonate-Vanadate with the Rutile Structure Vanadium dioxide Structural Phase Transition of VO,(B) to V02(A) Mechanism of n-Alkylammonium Ion Intercalation into the Layered Host a-VOP0,.2H20 Variable-range hopping Single-crystal Conductivity Study of the Tin Dichalcogenides SnS2 -xSex Intercalated with Cobaltocene Vermiculite Time-resolved Powder Neutron Diffraction Study of Thermal Reactions in Clay Minerals Vibronic Synthesis and Optical Spectroscopy of Platinum-metal-containing Di- and Tri-acetylenic Polymers Vinyl ether Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization.Part 13.-Synthesis and Living Cationic Polymerization of (S)-(-)-2-MethylbutyI 4-(o-Vinyloxy)-Groups Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization I5 Viscosity.Vitrification in Low-molecular-weight Mesogenic Compounds.Preparation and Characterization of wholly Aromatic para-Linked Copolyamides of Poly(p-phenyleneterephthalamide) Vitrification Vitrification in Low-molecular-weight Mesogenic Compounds X-Ray diffraction Dealumination of Hexagonal Polytype of Faujasite by Treatments with Silicon Tetrachloride Vapour Thermal and X-Ray Diffraction Studies of Liquid Crystals Intercalation of 2-Aminoethylferrocene into the Layered Host Lattices MOO 2H-TaS2 and a-Zr(HP04)2*H20 X-Ray Diffraction Characterization of Iridium Dioxide Electrocatalysts Transformation of Schoepite into Uranyl Oxide Hydrates of the Bivalent Cations Mg2+ Mn2+ and Ni2+ Crystal Structures of Chiral Smectogenic 4-Octylbiphenyl-4-y1 p-Methylheptyloxy]biphenyl-4-carboxylate,667 Studies of Non-linear Optical Organic Materials Crystal and Molecular Structure of 2-Dicyanomethylene- 1,3-dioxolane I057 X-Ray photoelectron spectroscopy X-Ray Photoelectron Spectroscopy of New Soluble Polyaniline Perchlorates Evidence for the Coexistence of Polarons and Bipolarons Analytical Characterization by X-Ray Photoelectron Spectroscopy of Quaternary Chalcogenides for Cathodes in Lithium Cells Y-Ba-Cu-0 system Metal-to-non-metal Transitions in High-temperature Oxide Superconductors monitored by Photoelectron Spectroscopy Structure Evolution during Thermal Processing of High-T Ceramic Superconductors produced using Sol-Gel Techniques Room-temperature Electrochemical Reduction of YBa2Cu30 Low-temperature Synthesis of YBa,Cu,O Films by Solution Process using Y-Ba-Cu Heterometallic Alkoxide.Zintl phase Synthesis and Crystal Structures of the Layered I-III-V Zintl Phases K,In,X where X =As Sb Zirconia-ceria ceramic Effect of Nickel Oxide on the Sintering Characteristics and Phase Stability of Zirconia-12 mol% Ceria Ceramics Zirconium Synthesis Structure and Spectroscopic and Electrochromic Properties of Bis(phthalocyaninato)zirconium(Iv) Zirconium Compounds as Coatings on Polystyrene Latex and as Hollow Spheres Porous Chromia-pillared a-Zirconium Phosphate Materials Zr0,-La20,-Ta20 system Compound and Solid-solution Formation Phase Equilibria and Electrical Properties in the Ceramic System Zr02-La20Ta,O Copenhagen Opt(r)ode Workshop Roskilde Denmark Mrs Hanne Jensen MODECS Copenhagen Opt(r)ode Wdshop RIM National Laboratory,MILJKEM DK-4000 Roskilde Denmark. Tel. int.+ Ext. 5333. FAX EMRS1991Fall Meeting Strasbcurg France. P. Siffert EMRS Fall Meeting C. T. T. B. P.20,67037 Strasbourg,Cedex France Second Foresight Conference on Molecular Nanotechnology Palo Alto California USA Foresight Institute PO Box Palo Alto CA USA November 11-15 5th International KyotoConference on New Aspects of Organic Chemistry (IKCOC-5) (Session 2 Organic Synthesis for Materials Sdence) Kyoto Japan Professor Yoshiki Ohshiro Chahan of IKCOC-5 Dept of Applied Chemistry Osaka University Yamadaoka 2-1 Suita Osaka Japan. November 17-22 ICFRM 5 Fifth International Conference on Fusion Reactor Materials Clearwater Florida USA Dr E. E. Bloom General Chairman ICFRM-5,Oak Ridge National Laboratory,PO Box Building 4500-S Oak Ridge TN37831-6117 USA International Symposium on New Polymers Kyoto Japan Professor ToshinobuHigashiura Department of Polymer Chemistry Kyoto University Yoshida Sakyo-ku,Kyoto 606,Japan Electrical Optical and Magnetic Properties of Organic Solid State Materials (MRS Symposium) Boston,USA D. J. Sandman GTE Laboratories Incorporated,40Sylvan Road Waltham MA USA. Tel. (617) 466-4216 Cellulose'91 New Orleans,USA Dr Noelie R. Bertoniere USDA ARS SouthemRegional Research Center Robert E. Lee Boulevard PO Box New Orleans,LA 70179-0687 USA Recent Developments in Intercalation Chemistry London UK DrP.T. Moseley Harwell Laborato y,Didcot Oxon OX1 ORA. Tel. 432833; FAX Professor A. E. Underhill Department of Chemistry University of Wales Bangor Gwynedd LL57 2UW. International Conference on Molecular EIedronics Sdence and Technology US Viin Islands Charles V.Freiman Engineering Foundation East 47th Street,New Yo NY USA. Tel. (212) 705-7835. FAX (212) 705-7441 Protein Engineering Structure Prediction and Ugand Interactions London UK Dr Neera Brokakoti c/o Roche products Ltd,Broadwater Road Welwyn Garden City Hem AL7 3AY UK Faraday Division Symposium on The Conformation Flexible Molecules in Fluid Phases Southampon,UK Professor G. R. Luckhurst Department of Chemistry University of Southampon Southampon so95NH UK Condensed Matter and Materials Physics Conference. Birmingham UK Sharon Keeley CMMP-9 Schoolof Physics and Space Research University of Birmingham Edgbaston Birmingham B15 2TT

ISSN:0959-9428    

DOI:10.1039/JM99101BP069

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 903-913 903 FEATURE ARTICLE Optical Properties of Sol-Gel Glasses doped with Organic Molecules Bruce Dunna and Jeffrey 1. Zinkb a Department of Materials Science and Engineering and Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90024, USA The sol-gel process enables one to prepare oxide glasses at room temperature with little or no heating. By using this method, it is possible to encapsulate a wide variety of organic and organometallic molecules in the inorganic matrix. Studies of this new type of organic/inorganic composite have evolved towards two different objectives: the use of luminescent molecules as probes of the sol-gel process and the deliberate doping of organics to produce materials with specific optical properties.This review emphasizes the ability of encapsulated luminescent molecules to provide unique insights regarding local chemistry and structure during the sol-gel- xerogel transition. The second part of this review gives several examples of how organic-doped sol-gel materials are emerging as an important means of producing photonic materials. Keywords: Sol-gel processing ; Organic molecule ; pH sensor; Chemical sensor ; Feature article The sol-gel process is a chemical synthesis technique for preparing gels, glasses and ceramic powders. The method has received considerable attention because it possesses a number of desirable characteristics. It enables one to prepare glasses at far lower temperatures than is possible by using conven- tional melting.Compositions which are difficult to obtain by conventional means because of volatilization, high melting temperatures or crystallization problems can be produced. In addition, the sol-gel method is a high-purity process which leads to excellent homogeneity. Finally, the sol-gel approach is adaptable to producing bulk pieces as well as films and fibres. During the past 5 years it has been widely recognized that the sol-gel process may be used to encapsulate organic and organometallic molecules in an inorganic medium. It is now evident that the synthesis of organic-doped gel-glasses is not limited to just a few organics. The flexible solution chemistry and the ability to prepare an essentially inorganic matrix with little or no heating means that the sol-gel approach is compatible with a wide variety of organic molecules.The list of organic-doped sol-gels is constantly expanding. Prior to the sol-gel work, the incorporation of organic molecules in solids generally was restricted to the use of frozen solvents or organic polymer matrices. The present approach represents a totally new type of organic/inorganic composite material because the oxide matrix not only offers a signifi- cantly more ionic environment but also it is thermally, chemi- cally and dimensionally more stable. Thus, studies of organic- doped sol-gels have begun to develop substantial breadth; from investigations of doped sol-gels for spectroscopic and matrix-isolation photochemistry, to the effect of solvent chem- istry on luminescence properties, to the development of lasers and non-linear optical materials.The present paper will review the research in the two most developed areas for organic-doped sol-gel glasses; the use of luminescent molecules as probes of the sol-gel process and the development of specific optical properties based on the properties of the organic dopants. The emphasis of the paper will be on the ability of luminescent molecules to probe local chemical and structural changes which occur as the matrix evolves from a sol through the sol-gel transition, the ageing process and the drying stage. Optical spectroscopic techniques are used to detect the changes and to interpret the chemical and structural environment responsible for them.The second part of the review will consider the aspect of inducing specific optical properties based upon the deliberately chosen dopant. This work has led to the development of optical materials that exhibit laser action, optical gain, chemical sensing and non-linear optical effects. Preparation of Inorganic Glasses by the Sol-Gel Method The synthesis of materials by the sol-gel process generally involves the use of metal alkoxides which undergo hydrolysis and condensation polymerization reactions to give gels. The synthesis of oxides by this approach has been the subject of several books and reviews and the reader is referred to this literature for more in-depth disc~ssion.'-~ In this section, an overview of the sol-gel approach is given that places an emphasis on those aspects which are particularly relevant for this paper.The sol-gel process can ordinarily be divided into the following steps: forming a solution, gelation, drying and den~ification.~In the preparation of a silica glass, one starts with an appropriate alkoxide [e.g. Si(OC2H5)4, tetraethyl- orthosilicate or TEOS] which is mixed with water and a mutual solvent, such as ethanol (EtOH), to form a solution. Hydrolysis leads to the formation of silanol groups Si-OH. These species are only intermediates as they react further to form siloxane Si-0-Si groups. An example of the formation of a silica gel by the organometallic route is as follows: Si( OC2H5)4 +4H20-+ +4C2 H 50H nSi(OH),+nSiO2 +2nH20 (2) In general, the processes of hydrolysis and condensation polymerization are difficult to separate.Numerous studies have been performed in this area, and there is good under- standing of the chemistry involved and how the reactions relate to gelation and structural evol~tion.~-~ There are several parameters that influence the hydrolysis and conden- sation polymerization reactions including the temperature, solution pH, the particular alkoxide precursor and solvent, J. MATER. CHEM., 1991, VOL. 1 and the relative concentrations of the alkoxide precursor, water and solvent. Another consideration is that catalysts (usually acid, but basic ones have been used as well) are frequently added to help control the rate and the extent of hydrolysis.The conditions under which the hydrolysis and conden- sation occur have a profound effect on gel growth and m~rphology.~?~It is well appreciated that one can produce linear polymers, branched clusters or colloids in the solution depending upon various factors including the H20:Si ratio and pH. Silicate gels prepared at low pH (<3) and low water content (< 4mol water per mol of alkoxide) produce primarily linear polymers with low crosslink density. Additional crosslinks form during gelation and the polymer chains become increasingly entangled. Silicate gels prepared under more basic conditions (pH 5-7) and/or higher water contents produce more highly branched clusters which behave as discrete species. Gelation occurs by linking clusters together.At still higher pH and excess water content, colloidal silica is formed. As the hydrolysis and condensation polymerization reac- tions continue, viscosity increases until the solution ceases to flow. The time to gelation is an important characteristic which is sensitive to the chemistry of the solution and nature of the polymeric species. This sol-gel transition is irreversible and there is little if any change in volume. At this stage the one- phase liquid is transformed to a two-phase ~ystem.~ The gels formed in alcohol are termed alcogels, while those formed in aqueous solutions are termed hydrogels. The gel consists of amorphous particles of variable size (5-10 nm or smaller) with an interstitial liquid phase.After gelation, gels are generally subjected to an ageing process during which the gels are kept sealed and very little solvent loss or shrinkage occurs. Condensation reactions continue, increasing the degree of crosslinking in the network and producing an increase in gel viscosity. Syneresis is frequently observed at this stage. ' T~ The drying process involves the removal of the liquid phase. Low-temperature evaporation is frequently employed and there is considerable weight loss and shrinkage. As evapor- ation occurs, drying stresses arise because of the differential strains associated with the pressure gradient in the liquid phase. A series of papers by Scherer have been directed at understanding the fundamental mechanisms involved in dry- ing.*-12 The drying stage is critical as the ability to dry without cracking serves to limit the sizes of monolithic pieces.The final stage of the sol-gel process is that of densification. It is at this point that the gel-to-glass conversion occurs and the gel achieves the properties of the glass. As the temperature increases, several processes occur including elimination of residual water and organics, relaxation of the gel structure, and ultimately densification, usually by viscous sintering. The temperatures involved depend upon the specific system. In the case of SOz materials, temperatures corresponding to a viscosity of 1013 P (ca. 1200 "C)are generally involved in the densification stage.The high temperatures required for densification generally will destroy any incorporated organic molecules. Probes of Chemistry In this section we review the use of spectroscopic probes to follow the gelation process through its various stages. The most important probes monitor solution water content, pH effects and thermal effects. For each of these types of probes we consider the nature of the measurement, the changes which are observed, and the interpretation of the spectroscopic Changes in Water/Alcohol Content The chemical changes that occur during the polymerization reactions are an important aspect of the gelation process which has been studied by using molecular probes. A particu- lar change which was used to follow the rate of gelation was the change in the water:alcohol ratio.As the hydrolysis reaction proceeds, alcohol is continuously being produced and the ratio of the amount of water to the amount of alcohol continuously decreases. It is desirable to probe these changes on the molecular level. Pyranine The fluorescence spectrum of pyranine, 8-hydroxy- 1,3,6-trisul- phonated pyrene, is sensitive to proton-transfer phenomena.' The molecule can be encapsulated in gel-glasses and retain its fluorescence properties in the materials. As discussed below, the fluorescence spectrum is sensitive to the proton acceptor ability of the medium surrounding the molecule and can be used to monitor changes in the water: alcohol ratio.The spectroscopy of pyranine was studied in control solu- tions consisting of water :isopropyl alcohol mixt~res.'~ The protonated form of the molecule emits in the blue region of the spectrum at 430 nm whereas the deprotonated form emits in the green at 515 nm. The relative intensities of the blue and green emission bands depend on the surrounding medium. In water-rich environments the green emission band domi- nates because water acts as a proton acceptor. In propanol- rich environments, the blue band is dominant because the pyranine remains protonated. The ratio of the intensities, called F in our work, is defined as the intensity of the blue peak divided by that of the green peak.l4 The changes in the ratio, F, that accompany ageing and drying of the pyranine- doped aluminosilicate gels are shown in Fig.1. Consider first the initial part of the figure up to a processing time of ca. 150 h. F increases smoothly during the gelation process from t=O to an intermediate value of Fx0.45 at t= 15 h at the gel point. The ratio continues to evolve in closed gels over a period of time equal to ca. eight times the gelation time, eventually reaching a maximum value of Fx0.9 after 200 h. These results indicate that changes in the gel chemistry continue well beyond the gelation period. The macroscopic rigidity observed at the gel point does not mean that the reactive entities are immobile at the microscopic level. The rates of the reactions involved in the aging of the gel appear to be slower than those in the liquid state, but the extent of these changes is as great in the gel state as in the liquid state.after drying at 70 "C ->*# I drying 0*5Y0.0 : I I I I' I 0 100 200 300 400 tlh results in terms of the chemical changes during gelation, Fig. 1 Evolution of the emission intensity ratio (F) during gelation, ageing and drying. ageing and drying processes l4 J. MATER. CHEM., 1991, VOL. 1 Drying experiments were carried out after the luminescence of the sealed gel reached a stable value.14 F decreased slowly from 0.9 to 0.7 during the first 60% of weight loss. In contrast, the curve became irregular when the weight loss reached 70%. At this stage F increased sharply to a maximum of 1.6.This value is comparable to that observed for a gel that has been heated for 10 h under vacuum at 70 "C and is well dried. The spectral changes that occur are significant despite the fact that aluminosilicate sols do not undergo significant compositional changes. These results suggest that the pyranine molecules are probing a very selected aspect of the gel polymerization chemistry which is strongly influenced by the protonation/deprotonation characteristics of the solvation shell. The initial value of F just after hydrolysis is substantially different from that in a water-propanol mixture with the same water concentration. In the early moments of the gelation process, pyranine is not homogeneously distributed in the solution. Rather, it appears that the probe is already part of the small particles which result from partial conden- sation of the Al-OH groups.These particles, which have both water and pyranine molecules adsorbed, constitute a medium with a substantially higher proton donor ability than the average composition of the sol. The continuous changes in F during gelation and ageing indicate that significant chemical modifications occur both in the adsorbed layers and consequently in the solvation sphere of the pyranine molecules. The increase in F from 0 just after the solution preparation to 0.45 at the gel point and eventually to 0.9 at the end of ageing indicates that the proton-accepting ability of the adsorbed layers on the polymer surface decreases substantially.Ultimately an equilibrium is established that reflects the initial composition of the sol. The changes in emission during the drying of the gels can be explained on a similar basis. Propanol is the most abundant solvent present in the pore system of the gel and has a higher vapour pressure than water. The first step of drying corresponds to the vaporization of propanol which gives rise to an increase in the relative concentration of water in the remaining solvent. F decreases accordingly. Later as drying continues, the free water content approaches zero and F increases sharply. It must be emphasized that the above results are specific to aluminosilicate gels. The changes in the fluorescence spectra of pyranine were used to study the effect of pH on water consumption in the early stages of gelation of silicate glass prepared from tetramethyl orthosilicate (TMOS)." The most important result of this study was the demonstration that there is a slower decrease in water content at higher pH values.This conclusion was explained in terms of gradual changes in the rates of the opposing processes of water consumption and water release with pH. For example, at pH 2.5, the probe shows that the rate of increase in water content was significantly slower than the initial rate of con- sumption. However, as the pH increased, hydrolysis slowed down and condensation accelerated. It was noted that in the pH range 2.5-7.6, all polymerization reached a similar water content, estimated at 30-35%, after ca.6 h. Thus, it was concluded that the rate of water release by condensation is less affected by pH than the hydrolysis rate. Europium(@ and Terbium(@ The luminescence of europium(II1) ions was used to follow the sol-gel tran~ition.'~?'~ The total luminescence from the 'Do state exhibited a gradual increase in intensity as a function of both time and temperature of dehydration for TMOS gels. In addition the specific 5DO-+7F1 transitions showed a relative increase in intensity. This behaviour was explained in terms of formation of a chemical bond between the Eu"' and the oxygens of silicate groups. It was proposed that the metal ion acquires a symmetry similar to that in glasses obtained by melting silica. The formation of glasses prepared from TMOS and TEOS was compared by using the Eu"' probe.In these studies the peaks arising from the transitions 5Do-7F1 and 5Do-7F2 were compared. It was concluded that glasses prepared from TEOS are more dense and that the probe ion is surrounded sooner by the silica groups which replace water than in glasses prepared from TMOS. Effects of pH Coumarin dyes have been used to probe the effects of pH on sol-gel processing. Many coumarin dyes are luminescent when incorporated in silicate and aluminosilicate matrices. The dyes that have been studied and the positions of their emission maxima are given in Table 1.'* In all cases small shifts in the positions of the maxima from those found in solution are observed.Of all of the dyes studied, only coumarin 338 lost its luminescence properties in the silicate xerogel (Table 1). In aluminosilicate xerogels all of the coumarin dyes retain their luminescence properties. Significant shifts of the emission and the excitation spectra as well as the presence of new luminescence bands are observed for these dried gels. For example, coumarin 540 exhibits a new peak at 540nm in the dried gel whereas only one peak at 504 nm is observed in the aged gel. In order to examine the effects of the matrix and pH on the luminescence spectra of coumarin dyes, the luminescence of coumarin 4 in aged and dried silica gels was examined in detail. Coumarin 4(7-hydroxy-4-methylcoumarin) belongs to the family of hydroxycoumarins whose fluorescence properties depend strongly on pH." The neutral form of coumarin 4 shown in Fig.2 is the dominant species in aqueous alcoholic solutions for a wide range of pH and water contents. The various reactions leading to the species responsible for the fluorescence are shown in Fig. 2.20*21In neutral and alkaline regimes (pH>6) the fluorescence is mainly composed of a strong blue emission at 440-450nm from the anionic (A*) form. As the acidity is increased, there are two posssible sites of protonation. Protonation at the phenolic oxygen leads to the neutral molecule (N*) with emission at 390 nm while Table 1 Luminescence band maxima of coumarin-doped gels ( mol dm-3) and xerogels band maxima/nm coumarin silicate gel silicate xerogel aluminosilicate gel aluminosilicate xerogel 4 395,430, 486 421, 486 394, 420,488 399,420 338 494 - 482 509 440 426 419 426 428 460 450 439,476 443, 469 445,469 523 495 496 504 493 540 508 525 504 512, 540 540A 530 512 GROUND STATE y3 HOmo neutral form EXCITED STATE anionicform neutral form y-43 y 3 +H HO HO OH zwitterionicform cationic form Fig.2 Molecular structure of different forms of coumarin 4 and the corresponding acid-base equilibriaI8 protonation at the carbonyl oxygen leads to the zwitterionic form (Z*) which emits at 480nm. Another form of the zwitterion which emits at 530 nm has also been reported.22 In very strong acid, the second protonation will lead to the cationic form (C*) which has an emission peak at 412 nm.The luminescence spectra in the gels are different from those observed in solutions. The differences suggest that the dye is not simply dissolved in solvent-filled pores in the gel. Previous work with pyranine in aluminosilicate gels indicated that the organic molecule tended to be adsorbed on the gel particles during polymerization.14 In this regard it is import- ant to recognize that the variation of pH will change the composition of the gel surface. Colloidal silica has an iso- electric point at pH 2.2,23and only relatively small deviations from this value would be expected for silicon oxide based polymer structures. At low pH (<2.2) the net charge of the silica network is expected to be positive owing to the presence of Si-OH; groups on the surface of the gel particles.In contrast, at pH >2.2, the presence of Si-0- anionic groups is expected to produce a negative charge. The changes of the surface composition lead to changes in the interactions between coumarin 4 and the gel matrix and subsequently cause the luminescence of aged and dried gels to differ substantially from the luminescence in solution. For gels synthesized at pH <2, the protonated gel surface leads to a more acidic environment than that of the reference solvent (ie. with 20% water). At pH 0.2, the cationic form is observed in gels [Fig. 3(a)],but not in the reference solution, while at pH 1 [Fig. 3(b)],the spectrum for the aged gels is comparable to the more acidic pH 0.2 emission for the 20% water-ethanol solution." When the gel is prepared at a pH >2.2, the emission spectrum resembles that of the reference solution at higher pH.It should be recognized, however, that in aged gels the solvent is still present in the matrix and that it is likely that the dye molecules will be solvated. The luminescence of xerogels differs from that of aged gels in two important respects. First, the luminescence intensity from xerogels is greater because gel shrinkage produces an increase in dopant concentration. Both the absorbance and J. MATER. CHEM., 1991, VOL. 1 the luminescence intensity increase. The second important spectral difference is that the relative intensities of specific emission bands show substantial changes as drying occurs.These changes cannot be explained by considering the compo- sition of the interstitial liquid phase of the gel. Rather, the changes in relative peak heights are due to enhanced dye/ matrix interactions as compared to aged gels. The role of the dried gel matrix is to control effectively the environment of the coumarin molecule. The surface character- istics of the gel produced by the pH during gel synthesis become even more important in establishing the luminescence characteristics. At pH <2, the peak heights for C*in the dried gel increase substantially from that of the corresponding aged gel [Fig. 3(a) and (b)].The gel prepared near the isoelectric point at pH 2.5 shows a marked growth during drying of the luminescence peak for the neutral species, N* [Fig.3(c)].In the most negatively charged gel (pH 3.8), peaks from both the neutral and the basic forms increase in intensity. The reasons for the enhanced interaction in the several gels prepared under different pH conditions arise from the chemi- cal and structural changes which occur during drying. First, the solvent loss during drying decreases the concentration of molecules which are likely to solvate the dye and the active sites on the gel surface. Secondly, the gel shrinks and the pore system collapses. The net result of these two processes is that the dye molecules are forced into increased contact with the gel surface and the screening effect of the solvent is diminished. Thus, drying the gels synthesized under the most acidic conditions leads to an increase in the intensity of the band from the protonic form of coumarin 4.Drying the gels synthesized under less acidic conditions causes an increase in the intensity of the bands from the neutral and the anionic forms. Chemical Changes during Heating and Drying The electronic absorption spectra of cobalt@) complexes have been used to follow the transformation of gels into dried glasses by heating.24 The cobalt(I1) ion forms complexes with both octahedral and tetrahedral geometries. Less regular co- ordination geometries are also known. Because the absorption spectra of the complexes with the different geometries are drastically different, the spectra are a sensitive means of following changes in the co-ordination as the environment changes. The geometry of the cobalt(I1) complexes in the sol precursor is primarily octahedral.The absorption spectra show intensit- ies higher than that of Co(H20)Ef. When the gel is dried at 60 "C, the geometry remains octahedral. However, at tempera- tures between 200 and 600 "C, the metal ion adopts a lower co-ordination number and the spectrum shows three strong absorption bands. Analysis of the spectrum showed that it does not consist merely of a mixture of octahedral and tetrahedral species. It was suggested that the species at high temperatures might be a distorted five-co-ordinate complex. The detailed and intricate spectroscopic changes that occur were not simple to interpret, and the assignment of the bands was not definite.The studies provide an interesting method of following the gel-glass process through relatively high temperature regimes. They also indicate that the analysis of optical spectra of metal complexes in the inorganic matrix will be a fascinating area of research. Probes of Matrix Rigidity Rigidochromism as a Probe of Gelation, Ageing and Drying2' The rigidochromic molecule bipyridyltriscarbonylchloro-rhenium(I), ReCl(CO),bipy, is a probe of the changes in J. MATER. CHEM., 1991, VOL. 1 = 340 400 500 600 340 400 500 340 400 500 600 340 400 500 600 I/nm I/nm Fig. 3 Luminescence spectra of silicate gels synthesized at different pH doped with coumarin 4 mol dm-3).'8 The spectra are shown for aged (a) and dried (d) gels.pH: (a)0.2, (b) 1, (c)2.5, (d) 3.8 rigidity of sols and gels prepared from TEOS and diisobutoxy- aluminotriethoxysilane (OBu),AlOSi(OEt), (or ASE). Rigi- dochromism, defined as the changes in the energy of the 600 luminescence maximum as a function of the rigidity of the surrounding medium,26 was measured in fluid and solid (frozen) reference solvents to calibrate the magnitude of the 1580 .:-2.09):effect. Above the freezing point of the solution, the emission maximum is 605nm. As the temperature is decreased, the I--g 560 .-emission maximum is virtually unchanged down to a tempera- ture of ca. 180 K.A sudden blue shift is observed in the region of the freezing point of the mixture. The band maximum in tn .-5 540 -1 .o the frozen solution is ca. 530 nm. The changes were then used to probe the rigidity of the two systems during gelation and drying. These studies revealed large differences between the two systems. Probing the Aluminosilicate Sol and Gel The band maximum of the emission of ReCl(CO),bipy in ASE exhibits large shifts at various stages of the gelation and drying processes. The shifts of the position of the band maximum and changes in the weight of the sample as a function of time are shown in Fig.4. For convenience, the processing time is plotted on a logarithmic scale. The emission lo-' 1oo 10' 1o2 1o3 tl h Fig. 4 Wavelength of the emission maxima of ReCl(CO),bipy in the aluminosilicate system as a function of processing time; 0, the concomitant weight changes2' them related to a specific sequential step of the sol-gel transformation: gelation, ageing and drying.First, during the gelation stage, the most drastic chemical and physical changes occur. Interestingly, the ReCl(CO),bipy probe molecule is band in the liquid state just after the mixing of the components /, is broad and centred around 600 nm (v = 16 660 cm- ',Avl insensitive to these changes and the emission peak maximum = remains constant at 590 nm. This observation indicates that although the system is macroscopically solid, the rigido- 2500 cm-'). No change is observed at the gelation point, although the solution has turned to a solid amorphous material which does not flow when the container is tilted.After a long period of ageing in a closed container, the maximum emission is blue-shifted to 560 nm (v = 17 860 cm- ', Avl/,=365Ocm-'). At the end of the drying, the emission peak has shifted to 523 nm (v= 19 120 cm-') and has a width of ca. 3580 cm-'. The small change in the FWHM indicates that the position of the band maximum has uniformly shifted and that the effect is not caused by the growth of a new band with a concomitant decline of the original band. The evolution of the ReCl(CO),bipy luminescence shown in Fig.4 can be separated into three distinct parts, each of chromic molecules are unconstrained in a solvent-like environment. The second step of the process, the ageing period, takes place in a sealed vessel.Although the gel is kept in a closed container and no evaporation of the organic molecules occurs, the luminescence maximum continuously shifts to the blue. At the end of the ageing period, the emission maximum stabilizes at 560 nm, intermediate between the value observed in a completely fluid medium, 600 nm, and that in a completely solid medium, 525 nm. The blue shift during this period is caused by partial rigidification of the gel on the molecular level. The rigidochromic probe is not simply surrounded by the interstitial liquid phase as it was during the gelation stage, but now it becomes entrapped in the oxide polymer network.The third stage of the process, which is related to the final changes of the emission of ReCl(CO),bipy, is the drying of the gel. When the solvents are removed, the gel structure collapses and the gel shrinks continuously. The final volume is about one eighth of that of the aged gel. As indicated by the blue shift of the emission of ReCl(CO),bipy, this step is accompanied by a progressive and eventually complete rigid- ification of the matrix. The final emission wavelength is the same as that in frozen ethanol solution. Both the increase in surface energy due to modification of the interface between the oxide polymer and the liquid and the capillary forces of the solvents provide the driving force for this partial densification.New condensation reactions occur because some reactive groups are in closer proximity. As a result, the oxide network becomes more compact. Its flexibility drastically decreases with the departure of the solvating species. The ReCl(CO), bipy molecules, which were previously entrapped in the network, are now completely immobilized by this collapsing structure. Probing the TEOS Sol and Gel The same procedure is followed for the preparation of silica sonogels containing the rigidochromic probe. However, the TEOS system doped with ReCl(CO),bipy exhibits a very different behaviour. From the initial liquid state to almost the end of drying, the emission maximum remains fixed at ca. 600nm. A blue shift occurs only with the final removal of the alcohol.The contrasting behaviour of the silica gel indicates that there are significant structural differences between the two kinds of investigated systems and that ReCl(CO),bipy is a sensitive probe of this difference. In the silica gels, the con- stancy of the emission at 590 nm indicates that the probe molecules are in a non-rigid environment during gelation, ageing and a major period of the drying. The fact that this behaviour is different from that of aluminosilicate gels is not surprising. Indeed, the chemistry of the precursors, the mech- anisms of polymerization and, therefore, the structure of the gels are different.'Y2 Moreover, the characteristics of the pore walls including polarity and electric charge are expected to be substantially different.This may change the interactions of the probe with the oxide network and consequently its position inside the gel structure. The adsorption of the probe on the surface of a pore once the water and ethanol are almost completely evaporated may account for the evolution of the fluorescence towards the characteristic blue shift of the rigidified state. Fluorescence Depolarization Fluorescence depolarization of the probe molecules DPH (1,6- diphenyl-hexa-l,3,5triene)and DPHPC (2,3-diphenylhexa- trienepropanoyl-3-palmitoyl-~-or-phosphatidylcholine)was used to study the rotational diffusion of the large probes during gelati~n.~~ The method is based on the idea that rotational motion of the probe during its emission lifetime changes the direction of the intrinsic polarization. If the molecule is held rigidly, the emission of these probes is polarized. If the molecule rapidly tumbles, emission from many orientations is observed and the polarization is scrambled.The depolarization provides a relative measure of the microscopic viscosity if the probe interacts with its environment. Several parameters define the degree of polarization of the emitted light.28 The most relevant parameter is the polariz- J. MATER. CHEM., 1991, VOL. 1 ation anisotropy, r The anisotropy can have maximum and minimum values of 0.4 and 0.0 for immobile and mobile chromophores, respect- ively. The mobility of a chromophore in isotropic media affects the polarization anisotropy as given by the relationship ro/r= 1+6Rz, where r is the experimentally determined ani- sotropy of the chromophore in the medium, ro is the exper- imentally determined limiting anisotropy of the chromophore in a rigid matrix, z is the emission lifetime of the chromophore in the medium and R is the rotational relaxation rate.The latter term is a measure of the rate at which the chromophore reorients between the time it absorbs and emits the photon. The reorientation rate is related to the viscosity of the medium. Ideally (4) where kB is Boltzmann's constant, T is the absolute tempera- ture, V is the molar volume of the chromophore and q is the viscosity of the medium. A given luminescent probe can be calibrated and thus used to probe the viscosity of a gel.Several factors may prevent the exact numerical values of the local viscosity from being obtained, but relative changes in the viscosity can be readily determined. The results of the study indicated that the fluorescence polarization signal of DPH is highly depolarized and that the amount is invariant during gelation and ageing. In contrast, the much larger DPHPC molecule detects the onset of gelation by an increase in polarization. It was concluded that DPH does not detect the growth of the polymer chains resulting in gelation because residual solvent-filled pores are sufficiently large to permit rapid tumbling and complete depolarization. On the other hand, the larger DPHPC molecule detects polymer growth but still experiences substantial rotational motion after gelation.We have carried out studies with MNPH [1-(4-nitrophenyl)-6-phenylhexa- 1,3,5-triene] doped in silica gels.29 No changes in polarization anisotropy (r) were observed while the gel samples, in sealed containers, proceeded through the stages of gelation and ageing. However, once solvent removal was initiated, progressive changes in r were observed as shown in Fig. 5. It is interesting to note that during the time that the viscosity increased by 10-fold, sample shrinkage was ca. 15%. These results clearly demonstrate the feasibility of using fluorescence polarization techniques to detect microviscosity in the gel. 0 200 400 600 tlh Fig. 5 Changes in polarization anisotropy of MNPH during sol-gel processing.The sample was opened for drying after CQ. 250 h J. MATER. CHEM., 1991, VOL. 1 Photochromic Gels and Glasses Photochromism is defined as the reversible light-induced colour change caused by absorption of a photon.30 The photochromic molecules which have been doped into sol-gel glasses undergo large structural changes after absorption of a photon. The rates of both the light-driven structural changes and of the back reactions are sensitive to the environment in the matrix. Aluminosilicate Gels Three derivatives of the photochromic 1',3',3'-trimethylspiro-[2H-1-benzopyran-2,2'-indoline]molecule,abbreviated BIPS, were studied in our lab~ratories.~' All three showed reversible photochromism in aluminosilicate gels.Of these, PNM-BIPS, l'-phenyl-6-nitro-8-methoxyBIPS was the most stable in the gels and gel-glasses and was studied in the most detail. Freshly prepared gels containing PNM-BIPS were clear and highly photochromic. Ageing of the gels did not significantly change the photochromic properties. Photo-chromic transparent solids of dimensions of 1 cm x 1 cm x 1 cm were easily prepared and studied. Transient absorption spectra of gels containing PNM-BIPS were measured. The visible spectrum is dominated by a band growing in at 590 nm when the sample is irradiated. Upon blocking the irradiation the band disappears over several seconds to leave the net zero transient absorption seen before the pump beam was unblocked. The total disappearance of the transient absorption band shows that the photochromism is reversible in the gel.The reversibility exists in gels 3 months old. The rate at which the transient absorbing species is formed and subsequently reverts back to the starting material was monitored near the maximum of the transient absorption spectrum at 632.8 nm by using an He-Ne laser. Upon exci- tation with a mercury lamp at wavelengths shorter than 4000A, the absorbance at 632.8 nm rapidly rises and then levels off as the irradiation continues. When the excitation ceases, the absorption gradually decreases. A plot of the transmittance at 632.8 nm of a PNM-BIPS gel is shown in Fig. 6. The plot shows the baseline transmittance before irradiation (A), the increase in the absorbance when the irradiation begins (A-B), and the decrease in the absorbance after the irradiation is stopped.(B-C). The figure shows the results for a 7 day old gel. A plot of the natural log of the absorbance as a function of time after the excitation ceased (point C) is linear. During the initial gelation of the aluminosilicate, no change in the rates of the rise or decay of the 16 950 cm-' absorption 0.6 0.5 8 0.4 f 0.3 v)a 0.2 0.1 0.0 0 20 40 60 80 100 120 tls Fig.6 Absorbance at 632.8 nm for an ASE gel containing PNM- BIPS. The excitation of the sample began at point A and continued through part B to part C at which time the excitation ceased. The decay of the absorption of the transient follows point C3' caused by the photointermediate is observed.As the gels age over a period of ca. 100 days, the lifetimes of the photointerme- diates slightly increase but do not undergo major changes. The solid gels are fully photochromic, i.e. the ring-opening reaction is not a sensitive probe of the polymerization and ageing processes. In contrast, a rigidochromic probe of the microscopic rigidity of the medium clearly indicated that the oxide skeleton becomes increasingly rigid during ageing.25 During drying, no change in rate constant is evident until some 70% weight loss has occurred at which point the rate increases. One explanation for the increase is that the BIPS molecule interacts with the wall of the pore. This interaction could then inhibit the ring opening. Another possibility is that the effective viscosity of the solvent increases as the fraction of solvent phase in the pores becomes small and just a thin film of liquid covers the pore wall.As previous studies have indicated, a viscosity increase can lead to an increase in the rate ~onstant.~' The increase in the lifetime of the inter- mediate during drying provides a sensitive probe of the changes occurring during the drying process. The rigido- chromic probe is also sensitive to the internal changes occur- ring during drying.25 It is interesting to note that drying to a weight loss of ca. 75% causes both the photochromism to cease and the rigidochromic emission to level out at its maximum energy.Silicon Dioxide and Modijied Silicon Dioxides Photochromic BIPS molecules have been incorporated in Si02 and various chemically modified Si02 matrices.32 The properties of the unmodified Si02 xerogels were similar to those of the aluminosilicate xerogels: the photochromism stopped and these materials cannot be used for practical applications. However, BIPS molecules retained their activity even at the dry stage when incorporated in modified silica xerogels prepared from Si(OC2H,)3CH2CH3 and from the copolymerization of TMOS with polydimethylsiloxanes under mildly basic conditions. In the case of the former xerogel, normal photochromism, i.e. a change from colourless to coloured upon irradiation, was observed. In the latter case, materials with reversed photochromism (coloured to colour- less) were obtained.The difference between the normal and the reversed photochromism was explained in terms of the differences in the properties of the pores in which the BIPS molecule is trapped. In the case of the normal photochromism, the pore has an apolar surface composed of Si-CH2CH3 groups which do not stabilize the coloured form, whereas in the case of the reversed photochromism, the pore surface consists of Si-OH groups and is similar to that of SO2 glasses. Photochromic glasses have several important uses depending on the rates of the transformations. For example, if the transformations are fast, the photochromic glasses can be used as optical switches. Light of one colour causes the change in the absorption spectrum of the glass which, in turn, transmits or blocks light of a second colour.If the transform- ations are very slow (on the order of years), then the photo- chromic glasses can be used as optical data storage media. Light of one colour is used to 'write' on the glass and light of a second colour is used to 'read' the stored information. In addition to these applications, photochromic glass can be used to form energy-conserving coatings, eye-protection glasses and privacy shields. The ability to prepare doped sol- gels in thin film form suggests that these materials may play an important role in the emergence of photochromic appli- cations. Excimers of Pyrene Chemical and physical changes that occur during the sol- gel-xerogel transitions have been studied by using pyrene as a photophysical pr~be.~~,~~ The luminescence spectrum of this molecule exhibits vibronic structure.The ratio of the intensities of the first to fifth peaks in the spectrum (Z1/Z5) is sensitive to the polarity of the environment. The ratio increases with increase in polarity. In addition, pyrene forms excimers, i.e. complexes between one pyrene in its lowest excited state and a second pyrene in its ground state. The intensity of the excimer emission increases with increase in the concentration of the molecule and with trapping in small pores. Both of these changes facilitate the intermolecular complexation. Changes in the emission spectra of pyrene and its excimer have been used to probe the sol-gel-xerogel transitions in TEOS and TMOS systems.In the case of TMOS gels, two general patterns of behaviour were observed depending on the water to silane ratio. At low ratios, geometric irregularity and porosity build up gradually along the whole process, resulting first in an increase in excimer emission intensity as aggregation becomes more pronounced, followed by a decrease in excimer intensity (but an increase in the monomer band) as pyrene molecules become isolated. At high water to silane ratios, a smooth surface was formed. These results suggest that polymerization-gelation occurs at low water to silane ratios whereas formation of a colloid followed by its gelation occurs at high water to silane ratios.Ethoxy groups slow down the polymerization in comparison with methoxy groups, but the reaction rates coincide once all of the alkoxy groups are hydrolysed. Thus, the gel-xerogel transitions in both TEOS and TMOS systems proceed at the same rate. The pyrene excimer disappears at the final xerogel state, proving that the sol-gel process is an effective method for isolating organic molecules. The changes in the polarity of the pyrene environment along the sol-gel process, as reflected by the Zl/Z5 ratio are due to pyrene aggregation and not due to the support itself. The fluorescence of pyrene probe molecules has also been used to follow the formation of micelles in sol-gel glasses.35 The 11/Z3ratio was different in the sol, gel and xerogel stages.When the concentration of sodium dodecylsulphate, the micelle former, was high, the ratio had values similar to those of solutions of micelles. This result suggested that micelles are trapped in the sol-gel glasses. Optical Properties of Doped Sol-Gel Materials Another significant feature of the sol-gel process is that it is possible to induce new optical properties based upon the deliberately chosen dopant. For example, the addition of laser dyes leads to a new solid-state gain medium while the addition of soluble organic polymers and molecules produces non-linear optical effects. In the following section we review progress in areas where the optical properties of sol-gel are already giving evidence of applications.Sol-Gel Lasers There has long been an interest in fabricating solid-state gain media containing organic laser dyes. Organic laser dyes possess several advantages over their inorganic counterparts including much larger cross-sections for absorption and emis- sion and lower threshold powers for laser action. Their gain characteristics and tunability in the visible spectrum are also quite attractive for device applications. Despite the advantages offered by solid-stage gain media, attempts to incorporate organic dye materials in polymeric hosts have met with limited success. In general, polymeric hosts have not exhibited the necessary thermal and mechanical properties, photostability or refractive index uniformity to become successful laser hosts. In contrast, inorganic glasses offer superior optical, thermal J.MATER. CHEM., 1991, VOL. 1 and chemical properties. The problem here is that the organic dyes cannot withstand the thermal conditions posed by the processing temperatures of conventional glasses. The sol-gel technique offers a low-temperature method for synthesizing amorphous materials which are essentially inor- ganic. Both the alkoxide precursors and the common laser dye families (coumarin, xanthenes, oxazines) are soluble in the same solvents, ensuring that the dyes could be incorpor- ated in the matrix without undesirable aggregation effects. A particularly attractive feature of these materials is that by providing the dye with an inorganic environment, increased photostability is possible.Research activities during the past 3 years have clearly established that tunable solid-state lasers based on sol-gel glasses can be achieved. A variety of laser dyes doped in different sol-gel matrices have demonstrated laser action. To date, different rhodamine, coumarin and perylene dyes have lased in a variety of matrices including silica, alumina, aluminosilicate, organic-modified silicates (ORMOSILs) and sol-gel composites.'8~36-4' A summary of solid-state sol-gel lasers, their dyes and wavelengths over which lasing occurs is provided in Table 2. The majority of the sol-gel laser studies have emphasized the demonstration of laser action. Specific laser characteristics have been explored in relatively few systems and only initial results have been reported.Tunability has been demonstrated in gels doped with sulphorhodamine B (SRB)39 and ~erylene.~~ The threshold for lasing has been reported for these systems and is in the range of 1-10 pJ, although one must be aware of the pump source for each of these measurements. Slope efficiencies show substantial variation among the systems. In the case of rhodamine-doped sol-gel materials, it is evident that slope efficiencies are substantially dependent upon the matrix. Values range from 2% for R6G in alumina films37 to ca. 25% for R6G in aluminosilicate xerogels41 to 30% in R6G/ORMOSIL.43 These values for R6G are still less than the 40% reported for aged silica gels.44 In the case of SRB, the slope efficiency for SRB/ORMOSIL was 39%,43 which is nearly twice as large as that reported for SRB in dried siica ge1.39 Photostability represents one of the most important issues for sol-gel laser materials.Photodegradation under laser action provides a rigorous assessment of this behaviour. R6G in alumina films exhibited a 50% output reduction in laser intensity within 600 pulses when pumped at 1 MW cm-2.37 R6G in ASE monoliths pumped at 1 mJ per pulse reached the 50% level in 1500 pulses (I Hz repetition rate) and continued to exhibit laser action after 40000 pulses.41 No specific results were reported for SRB/silica; however, there was an indication that photostability was relatively poor as thermal effects at low pumping rates (10 Hz) led to decreased output power.39 The photostability of dye-doped ORMOSILs have been studied in greater detai1.43*45 Recent work has shown that these materials possess substantially longer life- times and operate at much higher repetition rates than the other sol-gel systems or polymer hosts.Rhodamine 6G and SRB doped ORMOSILs reach the 50% laser output level after 1 1 000 and 14 500 pulses, respectively, when pumped at 95 pJ (8 kW)at 30 Hz. The future prospects for tunable lasers based on dye-doped sol-gel materials are extremely promising. The number of potential dyes and the versatility of the sol-gel process to achieve a favourable chemical environment for the dyes suggests that solid-state tunable lasers can be fabricated throughout the visible spectrum and into the near infrared.The recent photostability results with ORMOSILs have greatly surpassed the laser lifetimes obtained with polymer hosts and these characteri'stics are likely to improve by using J. MATER. CHEM., 1991, VOL. 1 91 1 Table 2 Summary of sol-gel laser systems oscillating range (peak)/ matrix coumarin 1 coumarin 102 coumarin 153 rhodamine B sulphorhodamine 640 rhodamine 6G coumarin 153 fluorescein BASF 241 (perylene derivative) rhodamine 6G rhodamine 6G coumarin 153 rhodamine 6G sulphorhodamine B rhodamine B nile blue ~~~~ ~ ~~~~~~ SiO," SiO," SiO," SiO, SiO, ASE ASE ASE MMA-impregnated SiO, ORMOSIL (EP/MA) ORMOSIL (EP)ORMOSIL (MA)ORMOSIL (MA)ORMOSIL (MA)ORMOSIL (MA)ORMOSIL (MA) nm 433-457 (444) 487-495 (491) 545-572 (558) 612-620 (618) 605-647 (621) 561-580 (569) 545-565 (555) 545-559 (552) 568-583 (575) 557-598 (568) 559-587 (571) 498-574 (525) 562-590 (570) 600-625 (609) 593-607 (598) 680-746 (696) pump source (Ajnm) ref.XeCl excimer (308 nm) 18 XeCl excimer (308 nm) 18 XeCl excimer (308 nm) 18 bXeCl excimer (308 nm)Dbl Nd :YAG (532 nm) 39 dye laser (540 nm) 41 dye laser (460 nm) 47 dye laser (5 1 1 nm) 47 Dbl Nd: YAG (532 nm) 42 dye laser (540 nm) 36 dye laser (540 nm) 36 dye laser (460 nm) 36 Dbl Nd :YAG (532 nm) 43 Dbl Nd: YAG (532 nm) 45 Dbl Nd:YAG (532 nm) 45 Dbl Nd: YAG (532 nm) 45 " Aged Gels.ASE =aluminosilicate. MMA =methyl methacrylate. MA =methacrylate. EP =glycidoxy. E. T. Knobbe, B. Dunn, P. Fuqua, F. Nishida and J. I. Zink, in Ultrastructure Processing of Ceramics, ed. D. R. Uhlmann, M. Weinberg and S. Risbud, Wiley, New York, in the press. dyes with enhanced photostability and optimizing both the synthesis techniques and matrix composition. Third-Order Non-linear Optical Materials There is a vital need for new materials whose x(2)and f3) (second- and third-order non-linear susceptibilities) can be used to produce the various non-linear functions necessary for such operations as optical information processing and optical data storage. In general, the desired non-linear material must not only possess large x(2)and f3) but also exhibit good chemical and mechanical stability, low optical loss, a high optical damage threshold and be fabricable into useful forms such as fibres and films.Since the non-linear optical properties of organics are frequently the highest known, the application of the sol-gel method to synthesize non-linear optical (NLO) materials is quite promising. In initial reports, the chemical flexibility of the sol-gel approach has enabled researchers to incorporate specific constituents (conjugated polymers, organic molecules) which provide third-order non-linear susceptibility within an essen- tially inorganic matrix designed to provide superior stability, optical properties and fabrication capability. The high degree of 7c conjugation found in conducting polymers makes them attractive candidates for third-order NLO materials because of the extended network of delocalized .n electrons.Although conjugated polymers have demonstrated large f3 ) coefficients, they generally exhibit poor processing characteristics and lack environmental stability. Two different methods have been used to incorporate conducting polymers into sol-gel matrices. Prasad and co-workers have successfully synthesized silica gel/conjugated polymer composites containing up to 50% (by weight) They used a water-soluble precursor of the conjugated polymer, poly(pphenyleneviny1- ene) (PPV), mixing it with the silica gel precursor and a common solvent. When it was heated above 140 "C the PPV precursor was converted to form the conjugated polymeric structure.High optical quality as-cast films were synthesized and a number of optical waveguide studies have been per- formed. At 1.06 pm, f3)z3 x lo-'' esu was measured by the degenerate four-wave mixing (DFWM) technique. Not only is this value comparable to those of conducting polymers, but the non-linear response time is in the subpicosecond range. Prasad also reported the fabrication of two-dimensional grat- ings using the silica/PPV films and demonstrated the feasibil- ity of using these films for optical recording.46 Another sol-gel approach has been used to synthesize polyaniline-doped silica gels.47 Polyaniline (or PANi) was selected because it can be made highly soluble in a variety of solvents.The PANi guest was incorporated into a silica sol host by dissolving the polymer into a mutually compatible solvent, N-methylpyrrolidone (NMP). This characteristic was used to prepare silica gel monoliths containing PANi or 2-ethyl PANi.48 The resulting material contained substantially less of the conjugated polymer (ca. mol dmP3) than the films obtained by polymerizing PPV. Despite the low concen- tration, DFWM measurements indicated that f3) for the material at 1.06 pm was ca. 30% of the value of a CS2 reference sample (i.e. x(3) x5 x 10-l3 esu). Since nanosecond pulses were used in these DFWM experiments, it is not yet established whether the f3) response is electronic or if there is a thermal contribution. Another method for producing NLO sol-gel materials has been to add organic molecules that exhibit large non-linear effects. The properties of the saturable absorber dyes fluor- escein, acridine orange and acridine yellow doped in sol-gel silica matrices were in~estigated.~~.~' The short luminescence lifetimes measured with these materials, however, led to sub- stantially larger saturation intensities than those of the dyes contained in low melting glasses.It was proposed that the presence of interconnected pores in the sol-gel matrix enabled oxygen quenching of the triplet state to occur. The use of 'composite' sol-gels, where the porous matrix is impregnated by an organic polymer thus eliminating the porosity, seems quite promising as long lifetimes were measured and low saturation intensities were calculated.Optically Based Chemical Sensors The overall requirements for a selective ion or molecular sensor are an indicator molecule that reversibly interacts with a target molecule with a high degree of specificity and that has some detectable property that changes when the target molecule has interacted. One of the most familiar types of chemical sensors are acid-base pH indicators that change colour when the target molecule (hydronium or hydroxyl ions) interacts with the indicator. Optically based sensors are especially convenient and accurate because changes in the absorbance or luminescence of the medium containing the sensor can be readily measured or even visually detected.Sol-gel glasses are almost ideal host matrices for optical chemical sensors. They have the obvious advantages of chemi-cal inertness, mechanical stability and optical transparency. More importantly, they are able to encapsulate the indicator molecule physically in pores in the glass such that these molecules are immobilized and cannot be leached out, while at the same time they are porous enough to allow transport of metal ions, solvent and other small molecules into the interior of the glass. The glasses can be fabricated into desired shapes and sizes such as monolithic blocks or thin films for specific applications. Several recent observations revealed the feasibility of mak- ing sol-gel glass based optical sensors. During our studies of pyranine as a probe of chemical changes occurring during gelation and drying, we discovered that luminescence of the pyranine probe molecule was sensitive to the surrounding en~ir0nment.l~Gas and liquid diffusion in the xerogel was very rapid owing to the interconnecting pores which represent approximately half of the gel volume.Avnir and co-workers found that the luminescence of molecular dopants in sol-gel glasses could be quenched by molecules and gases surrounding the glass.” Reisfeld” reported that oxazine- 170 doped in sol- gel glass films exhibited significantly different absorption and emission spectra depending upon whether the films were immersed in water or aqueous ammonia. The exciting out- growth of these observations is the feasibility of making glasses having optical properties which change in the presence of target molecules, i.e.of making sol-gel glass chemical sensors. The simplest chemical sensors which have been demon- strated to date are pH sensors because the response to the target ion is an easily recognisable colour change. Thymoph- thaleine,52 phen~lphthaleine’~ and phenol reds3 have been doped into TEOS-based gel-glasses. When the glass is immersed in appropriate acid-base solutions, the glasses change colour at the same pH values as do the indicators in solutions of the same pH. Response times are typically fast, on the order of 1 s for the phthaleines. Films having thick- nesses of the order of several thousand 8, have been coated on glass substrate^.'^ The films doped with acid-base indi-cators reversibly respond to pH in <1 s.Gel-glasses have also been made which respond to the presence of metal ions. All of the sensors reported to date have been studied in a very preliminary fashion, and details about the reversibility and response times are generally lack- ing. In some cases, colorimetric reagents such as dimethyl- glyoxime (for Ni2 +) and o-phenanthroline (for Fe2 +) have been incorporated in silica glasses and have been shown to produce the characteristic colour when exposed to the metal (red for both Ni2+ and Fe2+).52 In other cases, a metal ion (e.g. iron) has been trapped and the glass has been exposed to solutions containing hexacyanoferrate to produce intensely coloured Prussian blue.53 Luminescence of Molecules Luminescence has played a major role in the development of sol-gel optical materials.When researchers recognised the possibilities of incorporating organic molecules in sol-gel matrices, luminescent dyes were the first organics to demon- strate that the synthesis of these organic-doped inorganic materials was feasible. Dye-doped sol-gels represent the most widely studied systems. This paper has given several examples of how luminescent dyes are used as probes of both the sol-gel transformation and the accompanying chemical and matrix rigidity changes. The luminescence of dyes has J. MATER. CHEM., 1991, VOL. 1 also been highlighted in the development of specific optical properties including laser action, optical gain, chemical sensing and non-linear optical effects.It should be noted that many other organic molecules have been incorporated in sol-gel matrices and that sol-gel optical materials exhibit lumi-nescence throughout the visible regi~n.”.’~ One interesting aspect of the dye-doped sol-gel materials is the opportunity to use this approach for matrix-isolation purposes and to investigate the fundamental spectroscopy of the molecule in the sol-gel environment. Several of these studies have appeared and subsequently been used in the development of laser and non-linear optical proper tie^.'^*^^,'^ A molecule of interest is the tris(2,2’-bipyridyl)ruthenium(rr) cation. Ru(bpy)i+ has been widely studied because of its application in photochemical conversion for solar energy.The spectroscopic properties of Ru(bpy)g + in sol-gel were com- pared to those of the molecule in low-temperature glasses and in water.” Although the absorption spectra are similar for all the solids, the emission characteristics are quite different. The molecules in sol-gel materials exhibit lower lifetimes and quantum yields than the other glasses, but higher values than those in water. The interpretation is that the porous nature of the sol-gel matrix (50~01%) permits much more oxygen quenching and freedom of motion of the Ru(bpy)g + complex than occurs in the dense glasses. As discussed previously, the saturable absorber dyes were affected by similar microstruc- ture considerations. Another important luminescence property which is likely to generate more interest in the future is energy transfer.The sol-gel approach provides an opportunity to investigate dye- dye energy transfer in solid matrices. In recent work energy transfer from R6G to rhodamine B in alumina films was detected and enhanced laser emission from rhodamine B (N2 pumped) was observed.” Another type of energy transfer that has been demonstrated involved that between a dye and an inorganic ion. Genet et al. synthesized ThPO, gels using coumarin 460 as sensitizer and Eu3+ and Tb3+ ions as activators.60*61Excitation spectroscopy was used to verify the existence of energy transfer. In the case of the coumarin/Eu3 + samples, the maximum Eu3 + emission was observed using 0.1% of coumarin.Summary and Conclusions The ability to use the sol-gel approach to produce organic- doped gels and glasses is now well established. By using appropriate precursors and solvents, researchers have demon- strated that a wide variety of organic and organometallic molecules can be incorporated into sol-gel matrices. The work to date has, in general, evolved towards two different objectives. One direction has been to use the organic dopant as a luminescent probe of the sol-gel process. In this role, the probe molecules furnish substantial insight regarding local sol-gel chemistry and structure. The information obtained by the technique is in a dimensional regime between the molecu- lar-level resolution offered by NMR and the macroscopic- level results obtained by thermal and gravimetric methods.Moreover, the ability to use solution chemistry as a reference point for interpreting the spectroscopic response of the probe molecules in sols and gels provides a sound scientific basis for this work. The second direction of research, that of the deliberate doping of organics in sol-gels, is clearly emerging as an important means of developing new photonic materials. It is now evident that dye molecules, photochromic molecules and even conducting polymers are able to retain their specific optical properties in sol-gel matrices. Within a relatively short period of time several significant results have been achieved J. MATER.CHEM., 1991, VOL. 1 913 in the areas of tunable solid-state lasers, third-order suscepti- bility and photochromic behaviour. A new generation of optically based chemical sensors based on the tailoring of gel porosity is likely to be the source of the next dramatic results in this area. 28 29 30 31 M. Shinitzky and Y. Barenholz, Biochem. Biophys. Acta, 1978, 515, 367. M. Cox, B. Dunn, J. I. Zink, manuscript in preparation. R. C. Bertelson, in Techniques of Chemistry, Vol.ZZZ: Photochro-mism, ed. G. H. Brown, Wiley-Interscience, New York, 1971 and ch. VII, p. 100. D. Preston, T. Novinson, W. C. Kaska, B. Dunn and J. I. Zink, The authors are grateful for the support of this work by the National Science Foundation (DMR 9003080). Additional support has been furnished by Lockheed Corp.under the UC MICRO program. We greatly appreciate the many contri- butions of our students and colleagues: J. Altman, P. Fuqua, R. Kaner, W. Kaska, E. Knobbe, J. McKiernan, W. Nie, F. Nishida, S. Parveneh, J. C. Pouxviel, D. Preston, 32 33 34 35 36 J. Phys. Chem., 1990,94, 4167. D. Levy and D. Avnir, J. Phys. Chem., 1988,92, 4737; D. Levy, S. Einhorn and D. Avnir, J. Non-Cryst. Solids, 1989, 113, 137. D. Brusilovsky and R. Reisfeld, Chem. Phys. Lett., 1987, 14, 119. V. R. Kaufman and D. Avnir, Langmuir, 1986, 2, 717. K. Matsui, T. Nakazawa and H. Morisaki, J. Phys. Chem., 1991, 95, 976. E. T. Knobbe, B. Dunn, P. D. Fuqua and F. Nishida, Appl. Op., 1990,29,2729. 0.Stafsudd and S. Yamanaka. 37 Y. Kobayashi, Y. Kurokawa and Y. Imai, J.Non-Cryst. Solids, 1988, 105, 198. 38 B. Dunn, E. Knobbe, J. McKiernan, J. C. Pouxviel and J. I. Zink, References 39 Mater. Res. SOC. Symp. Proc., 1988, 121, 331. F. Salin, G. LeSaux, P. Georges, A. Brun, C. Bagnall and 1 2 3 4 L. L. Hench and J. K. West, Chem. Rev., 1990, 90, 33. C. J. Brinker and G. Scherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, San Diego, 1989. Sol-Gel Technology, ed. L. C. Klein, Noyes Publications, Park Ridge, NJ, 1988. L. C. Klein, Annu. Rev. Mater. Sci., 1985, 15, 227. 40 41 42 43 J. Zarzycki, Opt. Lett., 1989, 14, 785. R. Reisfeld, D. Brusilovsky, M. Eyal, E. Miron, Z. Burstein and J. Ivri, Chem. Phys. Lett., 1989, 160, 43. J. M. McKiernan, S. A. Yamanaka, B. Dunn and J.I. Zink, J. Phys. Chem., 1990, 94, 5652. R. Reisfeld, D. Brusilovsky, M. Eyal, E. Miron, Z. Burstein and J. Ivri, Proc. SPZE, 1989, 1182, 230. J. C. Altman, R. E. Stone, B. Dunn and F. Nishida, Photonics 5 6 7 W. G. Klemperer and S. D. Ramamurthi, in Mater. Res. SOC. Symp., 1988, 121. C. J. Brinker, J. Non-Cryst. Solids, 1988, 100, 31. C. J. Brinker and G. W. Scherer, J. Non-Cryst. Solids, 1985, 70, 301. 44 45 Tech. Lett., 1991, 3, 189. G. B. Altshuler, V. A. Bakhanov, E. G. Dulneva, A. V. Erofeev, O.V. Mazurin, G.P. Roskova and T.S. Tsekhomskaya, Opt. Spectrosc., 1988, 62, 709. B. Dunn, F. Nishida, J. C. Altman and R. E. Stone, in Ultrastruc- 8 9 10 11 12 13 14 15 16 17 18 G. W. Scherer, J. Non-Cryst. Solids, 1986, 87, 199. G. W. Scherer, J. Non-Cryst.Solids, 1987, 92, 122. G. W. Scherer, J. Non-Cryst. Solids, 1988,99, 324; G. W. Scherer, J. Non-Cryst. Solids, 1988, 100, 77. G. W. Scherer, J. Non-Cryst. Solids, 1989, 107, 135. G. W. Scherer, J. Non-Cryst. Solids, 1987, 89, 217. N. R. Clement and M. Gould, Biochemistry, 1981, 20, 1534; K. Kano and J. H. Fendler, Biochim. Biophys. Acta, 1978, 509, 289. J. C. Pouxviel, B. Dunn and J. 1. Zink, J. Phys. Chem., 1989, 93, 2 134. V. R. Kaufman, D. Avnir, D. Pines-Rojanski and D. Huppert, J. Non-Cryst. Solids, 1988, 99, 379. R. Reisfeld, J. Non-Cryst. Solids, 1990, 121, 254. D. Levy, R. Resifeld and D. Avnir, Chem. Phys. Lett., 1984, 109, 593. J. M. McKiernan, S. A. Yamanaka, E. T. Knobbe, J. C. Pouxviel, S. Parveneh, B. Dunn and J. I. Zink, J. Znorg. Organomet. Polym., 1991, 1, 87.46 47 48 49 50 51 52 53 54 ture Processing of Ceramics, ed. L. L. Hench and J. K. West, Wiley, New York, in the press. P. N. Prasad, Mater. Res. SOC. Symp. Proc., 1990, 180, 741. J. 1. Zink, B. Dunn, R. B. Kaner, E. T. Knobbe and J. McKiernan, in Materials for Nonlinear Optics-Chemical Perspectives, ed. S. R. Marder, J. E. Sohn and G. D. Stucky, American Chemical Society, Washington, D.C., 1991, ch. 36, pp. 541-552. F. Nishida, B. Dunn, E. T. Knobbe, P. D. Fuqua, R. B. Kaner and B. R. Mattes, Mater. Res. SOC. Symp. Proc., 1990, 180, 747. R. Reisfeld and C. K. Jorgensen, in Struct. Bonding (‘Berlin), 1991, in the press. R. Reisfeld, J. Non-Cryst. Solids, 1990, 121, 254. A. Slama-Schwok, D. Avnir and M. Ottolenghi, J. Phys. Chem., 1989,93, 7544. R. Zusman, C. Rottman, M. Ottolenghi and D. Avnir, J. Non- Cryst. Solids, 1990, 122, 107. J. I. Zink, B. Dunn and S. Yamanaka, unpublished results. D. Avnir, D. Levy and R. Reisfeld, J. Phys. Chem., 1984, 88, 5956. 19 20 K. H. Drexhage, Topics in Applied Physics, Vol. I Dye Laser, ed. F. P. Schaefer, Springer, Berlin, 1975. G. J. Yakatan, R. J. Juneau and S. G. Schulman, Anal. Chem., 1972, 44, 1044. 55 56 D. Avnir, V. Kaufman and R. Reisfeld, J. Non-Cryst. Solids, 1985, 74, 395. Y. Kobayashi, Y. Imai and Y. Kurokawa, J. Mater. Sci. Lett., 1988, 7, 1148. 21 S. G. Schulman and L. S. Rosenberg, J. Phys. Chem., 1979, 83, 4. 57 R. Reisfeld, M. Eyal and R. Gvishi, Chem. Phys. Lett., 1987, 138, 377. 22 23 24 A. Bergman and J. Jortner, J. Lumin., 1973, 6, 390. R. K. Iler, The Chemistry of Silica, Wiley, New York, 1979. R. Reisfeld, V. Chernyak, M. Eyal, C. K. Jorgensen, Chem. Phys. Lett., 1989, 164, 307. 58 59 R. Reisfeld, R. Zusman, Y. Cohenand and M. Eyal, Chem. Phys. Lett., 1988, 147, 142. H. Sasaki, Y. Kobayashi, S. Muto and Y.Kurokawa, J. Am. Ceram. SOC., 1990, 73, 453. 25 26 27 J. McKiernan, J. C. Pouxviel, B. Dunn and J. I. Zink, J. Phys. Chem., 1989, 93, 2129. M. S. Wrighton and D. L. Morse, J. Am. Chem. SOC., 1974, 96, 998; P. J. Giordano and M. S. Wrighton, J. Am. Chem. SOC., 1979, 101, 2888. R. Winter, D. W. Hua, X. Song, W. Mantulin and J. Jonas, J. 60 61 M. Genet, V. Brandel, M-P. Lahalle and E. Simoni, C.R. Acad. Sci. Paris, 1990, 311, 1321. M. Genet, V. Brandel, M. D. Lahalle and E. Simoni, in Proc. SPZE Con5 on Sol-Gel Optics, ed. J. D. Mackenzie and D. R. Ulrich, SPIE, Bellingham, WA, 1990, vol. 1328, pp. 194-200. Phys. Chem., 1990,94, 2706. Paper 1/03546K; Received 12th July, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100903

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6),915-918 (C6H,CH2NH3)2CrBr3.310.7:A New Insulating Ferromagnet with a Curie Temperature of 51 K Gigliola Staulo and Carlo Bellitto" lstituto di Teoria e Struttura Elettronica e Comportamento Spettrochimico dei Composti di Coordinazione del C.N.R., Area della Ricerca di Roma, Via Salaria Km.29.5, 1-00016 Monterotondo Staz., Roma, Italy A mixed-halide bis(benzylammonium)tetrahalogenochromate(II), (C,H,CH,NH3),CrBr3~310~7,has been synthesized and characterized. The compound crystallizes in the layered K,NiF, perovskite structure. It orders ferromag- netically at Tc=51 K, one of the highest critical (Curie) temperatures shown by magnetic insulators. A hysteresis loop typical of a soft ferromagnet has been obtained. At T=6 K, the remnant magnetization is 4.2 x lo3cm3 mol-' G and the coercive field is 130 G.Keywords: ferrornagnet; Insulator; Hysteresis The search for new insulators that order ferromagnetically with as high a critical temperature, T,, as possible represents an interesting target in solid-state chemistry. To date, few well characterized bulk ferromagnets are known and they are characterized by having low T,.' Very few exceptions occur; one example is represented by the series bis(alky1ammonium)- tetrachlorochromate(u), which have been found to order ferro- magnetically in the temperature range 37-42 K.' These materials are typical examples of two-dimensional Heisenberg ferromagnets. They crystallize in space groups closely related to the perovskite K2NiF4 str~cture.~ The deviation from this structure is mainly brought about by cooperative Jahn-Teller distortion of the corner-sharing C1- octahedra surrounding the high-spin (3d)4 Cr2 + ion.An antiferrodistortive displace- ment of the C1- ions in the basal plane is observed, i.e. the [CrCl,] octahedra are tetragonally elongated, with the princi- pal axes alternately along [loo] and [OlO] directions of the parent K2NiF4 unit cell.4 Layers of [CrCl,] corner-sharing octahedra are separated by double layers of alkylammonium cations, CnHzn+ 1NH3f. van der Waals forces operate between the ends of the organic substituents of two adjacent alkyl- ammonium ions. The corresponding bromide derivatives have also been isolated, and the Curie temperatures of these materials were found to be slightly higher than 50 K.5 So far no iodo-derivatives have been reported.In the literature only completely ionic A,CrI, are known,6 where A=T1+, In+, but they have a different structure, i.e. the crystal structure consists of isolated [CrI6I4- octahedra with the T1+ ions being eight co-ordinate. In an attempt to isolate and stabilize the corre- sponding alkylammonium iodo-compounds in the perovskite structure we thought it was worthwhile to synthesize solid- state solutions (RNH3)2CrXxY4-x, where X =Br and Y =I, 0 <x <4. Another reason for doing this is to clarify the role of the halide in the superexchange mechanism in these ferro- magnetic materials and therefore to determine T,.Here we report on the synthesis and magnetic properties of the first of the series: (C6H5CH2NH3)2CrBr3 .JO .,. Experimental Elemental analyses were performed by Malissa and Reuter Mikroanalytische Laboratorium, Elbach, Germany. Benzyl- ammonium iodide was prepared by a direct reaction between benzylamine in ethanol and HI in water (56%) in the ratio 1:1. The resulting solution was concentrated to a quarter of the total volume. White crystals were isolated and collected, washed with ether and dried under vacuum. The purity of the compound was checked by elemental analysis. Since the Cr" compounds are very sensitive to oxygen and moisture, all manipulations were carried out using Schlenck tube techniques7 under oxygen-free nitrogen.Synthesis of (C6HSCH2NH3)2CrBr3.310.~ The synthesis was carried out by using a method described previously.' To a hot solution of Cr" in glacial acetic acid (90 cm'), prepared by passing HBr gas through a suspension of finely divided electrolytic Cr metal (1 g, 1.94 x lo-' mol), was slowly added a stoichiometric quantity of benzylam-monium iodide (4 g, 3.0 x lo-' mol) in the same solvent. As the sample cooled, a yellow-brown polycrystalline powder of the title compound was isolated. Found: C, 26.49; H, 3.49; N, 4.23; Cr, 10.45; Br, 41.53; I, 12.94%. CI4HZON2CrBr3 requires: C, 27.09; H, 3.22; N, 4.51; Cr, 8.38; Br, 42.48; I, 14.31%. X-Ray Powder Diffraction The polycrystalline sample was sealed under nitrogen in a Lindemann tube, i.d.0.3 mm, and diffraction patterns were collected with a Philips Debye-Scherrer camera (Ni-filtered Cu-Ka radiation). Magnetic Susceptibility Measurements Magnetic susceptibility was measured by means of a commer- cial SQUID magnetometer, Quantum Design model MPMS down to 4.2 K. The polycrystalline sample was placed inside a Perspex cylinder, sealed under nitrogen and placed in a long polyethylene tube. This tube was then inserted in the sample holder. An external magnetic field of up to 5 T was supplied by a superconducting solenoid. Temperature measurements were based on a calibrated carbon glass resistor up to 40 K, and on a Pt sensor above 40 K. The susceptibility measurements were corrected for diamag- netism as calculated from the known diamagnetic suscepti- bility of the constituents of the title compound, i.e.-2.72 x lo-, emu mol- '. The temperature-independent susceptibility, zTrpwas also introduced and it was found to be 1 x~O-~emu mol-' Electronic Spectra Near-infrared and visible spectra were recorded on a Beckman DK 2A recording spectrophotometer. Powdered samples were placed between two quartz glasses and sealed in a dry box with glue. MgO was used as reference. The absence of a broad intense band centred at 450nm, typical of Cr"' impurities, was taken as a further purity check. Results The mixed halide (C6H5CH2NH3)2CrBr3 .310.7 was isolated and characterized by elemental analysis and X-ray powder diffraction. The golden brown compound is very sensitive to air and moisture, and samples must be handled in an inert atmosphere.The X-ray diffraction patterns were indexed in the space group Pbca, (Dl:),with the following unit-cell parameters:? a=7.9, A;b =32.3, A;c =7.8,, A.These data are similar to those found in the pure bromide derivative, the crystal structure of which has been solved.' The compound shows a crystal structure similar to that of (RNH3)2MX4, where R is an alkyl group, M a divalent ion, and X a halide." As mentioned in the introduction, they consist of layers of MX6 octahedra linked in a square array by sharing equatorial vertices. Two adjacent layers of [MX4];"- are separated by the diamagnetic alkylammonium cations, RNH;. In the pre- sent case the magnetic unit is represented by the chromophore [CrBr,I].The longest unit-cell parameter is related to the distance between the magnetic layers by a factor of 112. Electronic Spectra The diffuse electronic reflectance spectrum of the title com- pound, reported in Fig. 1, is characterized by an edge in the visible UV region, on which are superimposed two sharp spin-forbidden bands at 18.7 and 16.2 kK; there is a broad band in the near-infrared at 11.2 kK. This optical spectrum is typical of a six-co-ordinated Cr2+ ion, thus confirming the t The space group assigned for (CnHZn+,NH,),CrCl,, n= 1,2,3 is Cmca. The unit-cell c parameter for this space group corresponds to the b parameter of the Pbac space group. J. MATER. CHEM., 1991, VOL. 1 presence of a [CrX,] chromophore.The main feature of the optical spectrum is represented by the two spin-forbidden bands, which appear at the same frequencies as those observed previously in the tetrachloro- and tetrabromo-chromate(I1) salts. These are pure spin-flip transitions and have been assigned as electronic transitions in D,, symmetry: on the basis of the exchange intensity mechanism." The other feature is the presence of an absorption edge in the visible region, which in the corresponding chloro- and bromo-deriva- tives is shifted to the near UV. This feature can be ascribed to an LMCT charge-transfer band.'* Magnetic Properties High-temperature Region The thermal variation of the inverse of the magnetic suscepti- bility, recorded at 100 G, in the temperature range 50-300 K is shown in Fig.2. Above 100 K the magnetic susceptibility follows the Curie-Weiss law: =C/(T-0) with Curie and Weiss constants of 2.98 emu K mol-' and 74 K, respectively. The effective magnetic moment is nearly equal to the spin-only value, i.e. 4.90pB, and it is typical of Cr" in a high-spin d4 configuration. The positive value of 6 indicates that ferromagnetic interactions (Jij>0) dominate. The magnetic data above 60 K were analysed in terms of Rushbrook and Wood series expansion, appropriate for an S =2, two-dimensional quadratic layer ferromagnet, as modi- fied by Lines13 with the exchange Hamiltonian H = -JS1.S2: Ng2pi/x= 1/2k,T+ J(-4+9x-9.O72x2 +55.728~~ +160.704~~+1 16.64~~) (1) where x= J/k,T, J is the nearest-neighbour exchange constant and g is the Lande factor.The best fit for the curve (solid line in Fig. 2), obtained by using a non-linear least-squares Marquardt algorithm, gave the parameters J = 13 K, g= 2.00. The values of J for the series are reported in Table 1, together with the other magnetic and structural parameters. 0 100 200 I I I IIII TiK 400 600 800 1000 2000 A/nm Fig. 2 Thermal variation of the inverse magnetic susceptibility in the temperature range 50-300 K for a polycrystalline sample of Fig. 1 Room-temperature diffuse electronic spectrum of (C6H,CH2NH,),CrBr, ,,Io., [the solid line is a least-squares fit to (C,H,CH,NH,),CrBr, .,I0 .,; peak values shown in kK eqn. (1)l J. MATER.CHEM., 1991, VOL. 1 Table 1 Magnetic parameters and interlayer spacings of (RHN3),CrX,, R =alkyl and X =C1, Br, I (CH ,NH 3)2CrCl, (C2H5NH3)2CrC14 42 41 13.0 10.1 59 58 9.44 10.71 (C6H,CH ,NH &CrCl, (C6H5CH,NH3)2CrBr3 .3c10.7 37 49 10.6 12.5 58 62 15.71 16.10 (C,H5CH2NH3),CrBr, 52 13.1 77 16.03 (C6H5CH2NHd,CrBr3 .3IO.7 51 13.0 74 16.15 Low-temperat ure Region A sharp increase in magnetic susceptibility is observed as the sample is cooled below 70 K. To ascertain the presence of a ferromagnetic phase transition, the variation of the molar magnetization, M, us. temperature in a powdered sample has been measured. The zero-field cooled (ZFCM) and field- cooled (FCM) molar magnetization curves are shown in Fig. 3.The first is obtained by cooling to 6 K in a zero field, applying an external field of 5 G and then heating. The ZFCM curve shows a peak at T=51 K. The FCM curve, obtained by cooling the sample in a field of 100 G, shows a feature typical of a ferromagnetic transition. This behaviour has been observed previously on polycrystalline ferromagnets. l4 The variation of magnetization us. external field was then measured for the same sample below and above T,; the plots for two temperatures well below T,, i.e. T=6 and 20 K are shown in Fig. 4. An isothermal magnetization at T>>T,, i.e. at T= 100 K is also reported. Above T, the plot is linear, confirming that the system is in the paramagnetic state. The experimental l 000000000000 oooo +-J 7 -0 00 (3 0 12000 Y 0 0 20 40 60 T/K Fig.3 Magnetization us. temperature plots at applied magnetic field of 5 G (U)and of 100G (0) 0 0 000 values fit the magnetization M: for S=2, g= 1.95 and 8=71 K. Below T,, at T =6 K, the magnetization increases with increasing field and reaches 80% of the saturation value at 5 T. The saturation value is expected to be 23 300 emu G mol-for an S =2 system, as calculated from the relation Ms =NAgpB where NA is Avogadro's number. At T= 20 K the magnetization increases with increasing field and reaches half of the saturation value at 2 T. At 6 K the increase of M us. H is faster and the saturation is reached more quickly. To verify that the title compound is a bulk ferromagnet, a hysteresis loop has been performed at both temperatures.The plot recorded at T=6 K, in the external field range +0.2 to -0.2 T, is shown in Fig. 5. At this temperature the remnant magnetization, 2.e. the value at zero applied field, is 4.22 x lo3 cm3 mol-' G, i.e. ca. 20% of the saturation value. The coercive field, H,, corresponding to the value of that where M =0, is 130 G. At T=20 K the remnant magnetization is 1.75 x lo3 cm3 mol-'G and the coercive field is 50 G. Discussion (C6H,CH2NH3)2CrBr3.310.7 is a ferromagnet with T,=51 K. This value is high compared to that shown by other known ferromagnetic insulators.' From X-ray powder diffraction data a similar crystal structure to the pure bromide derivative is suggested.In this structure the Cr" ion is tetragonally elongated and six-co-ordinate. The long axes of the octahedra alternate at right angles in the basal plane. The compound features ferromagnetic nearest-neighbour exchange resulting from the cooperative Jahn-Teller effect, which constrains the unpaired eg electron of Cr" to the dZ2 orbital. The super- exchange pathway is via bridging halide anions between the half-filled d: orbital on one Cr" ion and the empty d,2-,,2 orbital on its neighb~urs.~ The halide ion in the plane plays a key role in the superexchange mechanism between the neighbouring Cr" ions, and the nearest-neighbour exchange constant J increases on passing from the pure chloride to the bromide derivative^.'^ This is mainly due to a larger extension of the bromide valence electron shell.Here the remarkable result is that the substitution of the bromide by iodide does not change the value of J and therefore the value of T,. A -1 5' I I 1 2 3 4 5 -0.2 -0.1 0 0.1 0.2 HIT HIT Fig. 4 Isothermal magnetization us. magnetic field at T =6 K (O), Fig. 5 Hysteresis loop M=f (H) for a polycrystalline sample of the 20 K (n)and 100 K (0) title compound at T=6 K more marked increase in T, would have been expected, as observed previously on passing from the chloride to the bromide derivatives. This suggests that the substitution of the iodide in the chromophore [CrBrJ] occurs in the axial position and not in the basal plane (where the nearest-neighbour exchange J is effective).A similar effect has been observed previo~sly.'~*'~ The peak observed at the magnetic phase transition deserves comment. In general, for a simple ferromagnet, the magnetization below T, should be constant and equal to the reciprocal demagnetizing factor multiplied by the applied magnetic field. This is caused by the spon- taneous formation of domains exactly compensating for the increase in spontaneous magnetization below T,. However, if the sample displays significant anisotropy and/or hysteresis, below T, the formation of domain walls will be prevented, leading to the magnetization curve shown in Fig. 3 (ZFCM curve).14 In the present case the low value of the remnant magnetization observed in the hysteresis loop excludes the latter hypothesis.Previously, a.c. magnetic susceptibility measurements as a function of temperature on polycrystalline samples of pure tetrabromo-and tetrachlorochromate(I1) derivatives showed similar peak^.^^,^ Furthermore, a.c. mag- netic susceptibility measurements on a single crystal of (C6H5CH2NH3)2CrBr3&lo ., showed a strong anisotropy between xII and xI to the c axis of the Cmca unit cell, with constant and ca. two orders of magnitude smaller than that in the c plane below Tc.I6The compound behaves then as a 2D easy-plane ferromagnet.? In conclusion we have obtained a new ferromagnetic insulator with a reasonably high value of T,. This has been achieved by using para- magnetic ions with a high S value, i.e. Cr", and by diluting t One of the referees suggested the possibility that the compound is a metamagnet.This is not the case because of the absence of a typical 'S' curve in the magnetization us. applied magnetic field. A nice example is reported in the literature," where metamagnetic +[Fe"'(C,Me,),]. [TCNQ]. -and ferromagnetic [Fe"'(C,Me,),]. + [TCNE].- compounds are reported. Fig. 3 and 4 of this paper provide evidence of the difference in the magnetic behaviour in these compounds. J. MATER. CHEM., 1991, VOL. 1 heavier halogens in extended two-dimensional perovskite structure. Attempts to isolate pure (RNH3)2Cr14, R =alkyl, are in progress. We thank C. Veroli for X-ray data collection and Dr. A. Testa for the SQUID measurements. References 1 See e.g.R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1985, p. 142. 2 (a) C. Bellitto and P. Day, J. Chem. SOC., Dalton Trans., 1978 1207; (b) C. Bellitto, P. Day and T. E. Wood, J. Chem. SOC., Dalton Trans., 1986, 847. 3 A. Wells, Structural Inorganic Chemistry, Clarendon Press, Oxford, 4th edn., 1975, p. 172. 4 P. Day, M. T. Hutchings, E. Janke and P. J. Walker, J. Chem. SOC., Chem. Commun., 1979, 71 1. 5 C. Bellitto, P. Filaci and S. Patrizio, Inorg. Chem., 1987, 26, 191. 6 (a)H. W. Zandbergen, Acta Crystallogr., Sect. B, 1979,35, 2852; (b)J. Solid State Chem., 1981, 38, 239. 7 D. F. Shriver, The Manipulation of Air-sensitive Compounds, McGraw-Hill, New York, 1969. 8 C. Bellitto, Inorg. Synth., 1986, 24, 188. 9 D. M. Halepoto, L. F. Larkworthy, D. C. Povey and V. Ramdas, Inorg. Chim. Acta, 1989, 162, 71. 10 See e.g. G. Chapuis, R. Kind and M. Arend, Phys. Status Solidi A, 1976, 36, 285. 11 C. Bellitto, H. Brunner and H. V. Gudel, Inorg. Chem., 1987, 24, 2750. 12 A. B. P. Lever, in Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1984, p. 203. 13 (a) G. S. Rushbrooke and P. J. Wood, Mol. Phys., 1958, 1, 257; (b)M. E. Lines, J. Phys. Chem. Solids, 1970, 31, 101. 14 (a) D. W. Carnegie Jr., C. J. Tranchita and H. Claus, J. Appl. Phys., 1979,50,7318; (b)R. L. Carlin, L. J. Krause, A. Lambrecht and H. Claus, J. Appl. Phys., 1982, 53, 2634; (c) M. Hitzfeld, P. Ziemann, W. Buckel and H. Claus, Phys. Rev. B, 1984, 29, 5023. (d) 0. Kahn, Y. Pei, M. Verdaguer, J. P. Renard and J. Sletten, J. Am. Chem. SOC., 1988, 110, 782. 15 P. J. Fyne and P. Day, Muter. Res. Bull., 1985, 20, 197. 16 C. Bellitto, Mol. Cryst. Liq. Cryst., 1989, 176, 465. 17 J. S. Miller, A. J. Epstein and W. M. Reiff, Science, 1988, 240, 40. Paper 1100332A; Received 23rd January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100915

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 919-922 Dielectric Relaxation in Hydroxypolyesters Enrique Sanchez Martinez,a Ricardo Diaz Calleja" and Klaus Wilhelm Lienertb a E.T.S.I.I. (U.P. V.), E-46071 Valencia, Spain BASF Lacke und Farben Ag, GroBmannstraBe 105, Postfach 280180, 0-2000Hamburg 28, Germany Dielectric spectra of a hydroxypolyester (I)and an imide-modified hydroxypolyester (11) are presented. In both cases two clearly defined zones of relaxation are shown. At the high-temperature side of the spectrum the a relaxation zone is produced by micro-Brownian motion of the main backbone and by free charges, and below room temperature, a complex fi secondary relaxation zone, showing indications of structure, is detected. Detailed analysis of the subglass relaxation zone is given and activation energies from an Arrhenius plot (In f vs. T-') are calculated for both polymers.By application to the low-frequency (high-temperature) side of the a relaxation of a transformation which converts permittivity E* into polarizability a* a new relaxation peak appears; this is attributed to the conductivity in the liquid state. Keywords: Hydroxypolyester; Dielectric relaxation; Polarizabilify Polymers have great importance in the electrical industry as by butyltitanate. The number-average molecular weight as insulators. From this point of view the analysis of the dielectric measured by GPC was 1758. relaxation ' behaviour gives crucial information for the devel- opment of these materials. In this paper we present a study Imide-modijied hydroxypolyester I1 of the dielectric relaxation in two polymers used as electrical In a standard three-neck flask, equipped with a stirrer, con- wire coatings.denser and a nitrogen inlet tube a mixture of ethylene glycol (4.6g), trihydroxyethyl isocyanurate (1 1.9 g), dimethyl tereph- Experimental thalate (1 0.2 g), 4,4'-diaminodiphenylmethane(6.9 g), trimel- litic anhydride (13.5 g) and butyl titanate (0.04 g) was heated The polymers are a hydroxypolyester (I) and an imide-to 200 "C. An imide-modified polyester with an OH number modified hydroxypolyester (11) and were synthesised as of 160-170 mg g-' KOH was obtained. The imide-modified follows. polyester dissolved in solvents such as N-methylpyrrolidone or cresol and dissolution was catalysed by butyl titanate.The H ydrox ypol yester I number-average molecular weight measured by GPC was In a standard three-neck flask, equipped with a stirrer, con- 1598. denser and a nitrogen inlet tube a mixture of ethylene glycol Molecular weight was measured using a gel-permeation (6.7 g), trihydroxyethyl isocyanurate (14.8 g), dimethyl tereph- chromatograph equipped with two PL-gel columns (25 cm thalate (25 g) and butyl titanate (0.04 g) was heated to 200 "C. long, particle size 5 pm, 1000 8, and 100 8, pore size), operated A polyester with an OH-number of 200-210 mg g-' KOH at 40 "C at a flow rate of 0.5 cm3 min-' N-methylpyrrolidone, was obtained. The polyester dissolved in solvents such as N-using polystyrene as standard. Tg for I and I1 were 71 and methylpyrrolidone or cresol, and dissolution was catalysed 132 "C, respectively. 0 I-0-CH2-CH2-N I ,c\ N-CH2-CH2-0-C '~~-O-CH2-CH2-OH 0 0o+c. CH2-CH2-O-~~~-O-CH2-CH2-OHY 'O 0 II 0 -CH2-N /c, N-CH2-CH2-O-!e!-O-CH2-CH2-OH I1A,.p=o 0 0 0 0 II Scheme 1 Dielectric measurements were carried out using a GENRAD 1620 bridge with a three-terminal cell from -130 "C to +130 "C or +180 "C in the frequency range 0.1-100 kHz.The samples were prepared by curing the products at 180 "C for 1 h in an oven. The films obtained were coated with silver to ensure good electrical contact. A three-terminal cell was used in a thermostatic vessel built by us. Experimental values were recorded from the bridge after 15 min, after which time thermal equilibrium had been reached.tan 6 reproducibility was > +2% and the permittivity values were reproducible to > &5%, taking into account the uncertainties in the micrometer measurements of the thickness and width of the sample. Results and Discussion The dielectric permittivity and loss of I and I1 are shown in Fig. 1 and 2. For the sake of clarity the permittivity is presented at only two frequencies and the high-temperature tail of the loss curve of I at 100 kHz is also omitted. The spectrum is complex in both cases. Two clearly distinguished zones of relaxation are seen in both polymers: at low tempera- tures a broad fl loss peak was observed which showed evidence of structure.This seems to be a complex relaxation process with several overlapping dielectric absorptions. A detailed description of the p zone for I as an example is shown in Fig. 3. In order to characterize the absorptions appearing in the p zone we have calculated the activation energy by means of an Arrhenius equation from a plot of lnf us. T-' (Fig. 4). The values obtained and the temperatures of the peaks at 1 kHz are given in Table 1 together with an estimate of the uncertainty in the activation energies. The higher temperature cr-relaxations in the two polymers are assigned to the cooperat- ive motions around Tg and because of this they possibly follow a Williams-Landel-Ferry (WLF) behaviour for the corresponding relaxation times. The loss curve for I shows two relaxation peaks at frequencies higher than 1 kHz at temperatures above 80 "C.The loss curves of I1 (10 kHz and 100 kHz) show a rapid increase above 140 "C indicating the high contribution of the conductivity to the loss curves. 21k -100 80 I60 -40 -20 cc) -10 p18 -6 -4 1' Fig. 1 Dielectric permittivity E' and loss E" of I: 0, 0.1 kHz; x, 1 kHz; 0,10 kHz; V, 100 kHz J. MATER. CHEM., 1991, VOL. 1 12 6-E' 4-2-1--120-80 40 0 40 80 120 160 TI'C Fig. 2 Dielectric permittivity and loss of 11: 0,0.1 kHz; x, 1 kHz; 0,10 kHz; V. 100 kHz 14. I 1 -140 -120-100 -80 -60 -40 -20 0 20 40 TI0C Fig. 3 tan 6 vs. temperature for I in the fl zone showing the complex structure of this absorption.0, 0.1 kHz; 0,1 kHz; 0,10 kHz; A, 100 kHz In order to characterize the a relaxation, we suppose that all the relaxation times around Tghave the same temperature dependence, and the same shift factor ~,=z~/z~,~,where T~ is,~ the relaxation time at To,given by the Voge12 equation mIn a,=A+-T-T, where a, is calculated from the horizontal shift of the exper- imental curves and m is related to the relative free volume 4 by B m= -4 (T-T,) (2) J. MATER. CHEM., 1991, VOL. 1 12-11 10-$‘9-* = 8-7 6-5-i“ I 41 2 3 4 5 6 7 lo3 KIT Fig. 4 Relaxation map for I (0)and I1 (0).a shows the relaxations associated to T,. p’, P” and 8”’ show successiverelaxations in decreasing order of temperature. (a) a (11), (b)a (I), (c) p’ (11), (6)p’ (I), (e)B” (I), (f)P”’(~),(dB”‘(~I) Table 1 Characteristics of the relaxations for I and I1 I I1 T/”C E,/kJ mol-’ T/”C E,/kJ mol-’ a 98 WLF 140 WLF B’ B” -24 -48 170f10 108& 10 -37 - 72f5 - p’” -128 26f2 -130 17+2 according to the Doolittle3 equation BIn q=A’+-4 (3) where B is assumed to be unity and q is the viscosity.On the other hand, the expansion coefficient of the free volume at T, is given by (4) where 4, is the free volume at the glass-transition temperature. Values for 4, and a, for both polymers are given in Table 2. The values for 4gare close to 2.5 x lop2,the predicted value by the theory. On the other hand a, values are slightly higher than the predicted ones.Returning to the a relaxation in 11, it is possible to obtain more information by using polarizability a* instead of permit-tivity &*. a* and &* are related by &*-1a*=---&*+2 (5) as proposed by S~aife.~This transformation has been exten-sively used ’q6 for charge-transfer complexes in order to show up relaxations hidden by the high conductivity on the low-frequency side of the loss permittivity, because they tend to highlight the low-frequency absorptions. In this sense it is valuable in helping to clarify the experimental results. The use of polarizability instead of permittivity has been Table 2 $K and aKvalues for I and I1 I 3.O 6.0 I1 3.7 7.4 921 where &,--I -4zN~ &,+2 3v and considering the response of a macroscopic sphere in terms of a time-dependent correlation of the dipole moment of the sample.The first term on the right-hand side of eqn. (6) represents the instantaneous polarization of the sphere, (p(O)M(O))is the equilibrium induced moment of the sphere, L is the Laplace transform, is the decay function and the left-hand side of eqn.(6) is the complex polarization of the sphere under consideration. The polarizability provides a macroscopic quantity, a*, by use of eqn. (5). Moreover, S~aife,~considering the relaxation behaviour in a spherical specimen, has pointed out that the effects observed in a non-periodic field are not present in a periodic one and for this reason the transformation E* into a* is fully justified.A polarizability representation of the macroscopic dielectric data give us the opportunity to com-pare different materials according to the fact that eqn.(5) is a method for ‘normalizing’ the data and a Cole-Cole plot of the two components of the polarizability (a” us. d)gives more weight to the low-frequency absorptions than those with shorter relaxation times. Accordingly, values of a’ and cl” for I1 have been calculated by means the of equations 3El‘(E’ -1)(d +2)+&”2. ,,, = &I‘ - (E’ +2)2+El’* ’ (&’ +2)2 +&“2 (7) the real and imaginary parts of a* are given by eqn. (5). The results are shown in Fig. 5 at three frequencies. Higher frequencies do not show significant peaks. Two peaks are clearly distinguished in a* at 0.1 kHz.The first corresponds 1.oc 100 120 140 160 180 T/”C Fig. 5 Dielectric and loss polarizabilities of I1 at three frequencies: 0,0.1 kHz; x, 0.2 kHz; 0,0.5 kHz to the inflexion in E" at 0.1 kHz, i.e. the a relaxation. A second peak ca. 10 times higher than the first can be seen at 163.5 "C; this corresponds to the high-conductivity (low-frequency) zone. The results are striking, but they are consistent with our previous experience of high-conductivity compo~nds.~,~ Thus the transformation given by eqn. (5) appears to be applicable also to polymeric systems for detecting relaxation peaks hidden by conductivity effects. R.D.C. and E.S.M. acknowledge Stiftung Volkswagenwerk for financial support. J. MATER. CHEM., 1991, VOL. 1 References N. G. McCrum, B. E. Read and G. Williams, Inelastic and Dielectric Eflects in Polymeric Solids,Wiley, Chichester, 1967. H. Vogel, 2.Phys., 1921, 22, 645. A. K. Doolittle and D. B. Doolittle, J. Appl. Phys., 1957, 28, 901. B. K. P. Scaife, Proc. Phys. Soc., 1963, 81, 124. E. Sanchez Martinez, R. Dim Calleja, W. Gunsser, P. Berger and G. Klar, Synth. Met., 1989, 30, 67. E. Sanchez Martinez, R. Diaz Calleja and G. Klar, Synth. Met., 1990,38, 93. R. H. Cole, J. Chem. Phys., 1965, 42, 637. Paper 1/00877C; Received 25th February, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100919

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 923-928 Study of Ion Exchange and Intercalation of Organic Bases in Layered Substrates by Vibrational Spectroscopy Part 1.-Inelastic Neutron Scattering, Infrared and Raman Spectroscopies of Ammonium-and Tetramethylammonium-exchanged a-Tin Hydrogen Phosphate Michael J. Hudson,*a Andrew D. Workman,a Deborah J. Jones,*' Bernard Bonnetb and John Tomki n sonc a Department of Chemistry, University of Reading, Whiteknights, Reading RG6 2AD, UK Laboratoire des Agregats Moleculaires et Materiaux Inorganigues, URA CNRS 79, Universite Montpellier 11, Place E. Bataillon, 34095 Montpellier Cedex 5, France Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQX, UK The nature of guest-host interactions has been studied in ammonium- and tetramethylammonium(TMA)-intercalated a-Sn(HPO,),*H,O(SnP), using a combination of infrared, Raman and incoherent inelastic neutron scattering spectroscopies, in order to obtain information on such characteristics as the extent of proton transfer from the acidic sites on internal surfaces to interlayer molecules, the relative freedom of movement of the intercalate, and the site symmetry of the guest species.Ammonium ions are strongly hydrogen bonded to the macroanionic layers and infrared activity suggests the site symmetry of NH, to be reduced from ideal tetrahedral. Combined techniques indicate the skeletal vibrations of exchanged TMA to have spectroscopic activities and positions similar to the corresponding halides. However, the positions of the CH, torsional modes in inelastic neutron scattering demonstrate their sensitivity to the macrostructural environment and are consistent with weak SnP-TMA interactions.Keywords: Layered phosphate; Ammonium ion ; Tetramethylammonium ion ; Incoherent inelastic neutron scattering; /on exchange The inorganic ion exchangers of general formula M'V(HA04)2-H20, MIV=Ti, Zr, Sn etc., A=P, As, and exemplified by its most studied member ~x-zr(HP0,)~ H,O(ZrP), are layered materials of basal spacing 7-8 A.' In addition to the vast literature on their ion-exchange character- istics,2 the transport properties of ZrP are now well docu- mented,, and structural studies not only on single-crystalline materials,, but also on gel and amorphous phases and the delaminated 'pellicular' form are a~ailable.~ Intercalation of organic molecules is also a well described phenomenon,6 which can be generalised to other classes of layered com- pounds, characteristically producing an increase in the inter- layer distance through expansion of the interlayer zone.Work in this area has concentrated largely on synthetic aspects including the identification of various intercalation com-pounds7 which exist in the sometimes complex phase dia- grams, with particular discussion focussing on the orientation of the intercalated species within the interlayer area.* Organic- inserted metal phosphates, especially amine intercalates, are being used increasingly as precursors for the synthesis of pillared layered compounds9 and in metal-extraction pro- cesses, by which full use of the metal exchange capacity may be achieved, lo and their protonic conduction properties are being identified under well defined conditions." Other characteristics inherent to such organic-inorganic composites include the nature of intercalate-substrate binding (van der Waals, hydrogen bonding, etc.) the extent of proton transfer to the inserted organic species, the relative freedom of movement of the intercalated molecule or ion, and the symmetry of the site it occupies. These questions can be usefully addressed using vibrational spectroscopy. For example, variable temperature FTIR measurements on ZrP intercalated 'with n-CH,(CH2),NH2, n = 11 and 13, have recently provided evidence for a departure from the strict room-temperature trans-planarity of alkyl residues at tem- peratures above 125 "C, by the formation of conformational kinks.l2 Using the structural analogue of ZrP, ~esn(HP0,)~ *H20 (SnP) as host material, for which detailed vibrational data are a~ailable,'~.'~we present here a combined study using infrared and Raman spectroscopies and incoherent inelastic neutron scattering of ammonium- and tetramethylammonium-inserted SnP. Neutron inelastic scattering (INS) is particularly useful in identifying vibrational or librational modes resulting from displacement of protons, while remaining essentially 'trans- parent' to vibrations of an aprotic host lattice, and so com-pletes the data available from optical spectroscopy.The first of the above compounds, 'SnP-NH,', can be considered as the end member of the family of primary-amine intercalates, whereas for the second the effect of complete methyl substi- tution for hydrogen atoms on nitrogen in this system will be demonstrated. Further papers in this series will deal with aliphatic saturated and non-saturated amines intercalated in layered substrates, including SnP. Experimental Synthesis SnP was synthesized according to the published procedure.' Its X-ray powder diffraction pattern (Spectrolab series 3000 CPS-120 instrument, Ni-filtered Cu-Ka =1S405 1 A) indicated a basal spacing of 7.8 A, and the absence of any impurity peaks. The intercalate SnP-NH, was prepared by direct reaction of SnP with ammonia gas by evaporation in a two- arm, slightly evacuated reactor from concentrated ammonia solution onto SnP.It was demonstrated earlier that the formation of ZT(NH,PO~)~ -H20 does not occur by H '/ NH: ion exchange (even from NH4C1-NH40H solution) but by diffusion of NH, to acidic sites.I6 This method gave an X-ray diffraction pattern corresponding to a single-phase compound of interlayer spacing 9.9 A, comparable to that reported previously for ZrP-NH,, 9.4 A.16 Elemental analysis indicated a complete reaction: Sn(HP04)2 *H20 +2NH3+Sn(NH4P04)2 -H20 (%N calc. 7.7, exp. 8.3). Alternative routes to SnP-NH, use NHZ (con- centrated ammonia solution) in direct reaction with SnP [l g SnP/100 cm3 NH3(aq), 3 h] or to displace allylamine from the interlayer zone in an SnP-monoamine intercalate precur- sor.Although the X-ray diffraction patterns of these materials, and that produced by diffusion of gaseous NH3, are identical, only by the last method is hydrolysis expected to be insignifi- cant. The spectra reported here result from samples prepared in this way. Half-exchanged SnTMAo.9-, .lH1 (P04)2*4H20 may be synthesized by prior swelling of SnP in propylamine and subsequent reaction with TMA ions in aqueous solution to replace alkylammonium ions.' However, the sensitivity of the INS method is such that any traces of non-exchanged propyl- amine would contaminate the spectrum. For this reason, direct, although less complete, intercalation of TMA was attempted.SnP was shaken with an aqueous ethanolic solu- tion of ionic TMA (1 g SnP/2 g TMAC1, 24 h) to give a material of interlayer spacing of 17.3 A, for which thermograv- imetric and elemental analyses indicated ca. 30% exchange H+/TMA. Spectral Measurements Infrared spectra of SnP, SnP-NH, and SnP-TMA were recorded at room temperature over the range 220-4000 cm -' as KBr discs on a Perkin-Elmer FTIR spectrometer, model 1720-X. Raman spectra were recorded with a Dilor spectrometer using an argon laser (4880 A, 400 mW) and the data processed through a Tracor TN 1710 modular multichannel computer (Northern Instruments). The samples were sealed in glass capillaries and were placed at room temperature in a rotating cell to avoid decomposition.Spectral resolution is 0.5-1.O cm -' over the entire range, 20-4000 cm -'. The INS spectra of SnP-NH, and SnP-TMA were recorded at 25 K using the time-focussed crystal analyser spectrometer, TFXA, at the spallation neutron source, ISIS, Rutherford Appleton Laboratory, UK. Samples were con- tained in an aluminium can, 5 cm x 2 cm, and mounted onto the cadmium sample holder at the lower end of the cryostat centrestick. In both cases, data were collected for ca. 800 pA h (ca. 10 h) of beam current at 25 K. Background subtraction over the range 16-4000 cm-l gave the spectra reproduced here. Further information on the characteristics of TFXA have been reported elsewhere.' Vibrational Spectrum of the Ammonium Zon Of the four fundamental internal vibrations associated with tetrahedral ammonium ion, the totally symmetric stretching v1 (al) and doubly degenerate v2(e) deformation modes are infrared inactive leaving the triply degenerate stretching (v3, t2) and bending (v,, t2) vibrations expected, from spectra of typical to occur at ca.3100 cm and 1400 cm-', respectively. All four modes are Raman active, the totally symmetric vibrations giving lines at 2800-3000 and 1650- 1750 cm-'. In addition to the internal vibrations, the triply degenerate mode v6 describing rotation of tetrahedral NH, is both IR and Raman inactive. The above vibrational spectrum can be affected by the nature of the crystal site, and in the particular case of the NH: ion, which has an appreciable tendency for hydrogen- bond formation, distortion of the crystal field can occur leading to reduction in site symmetry.Hydrogen-bond forma- J. MATER. CHEM., 1991, VOL. 1 tion also frequently lowers the co-ordination number of ammonium to 4 or 5, where 10 or 12 might have been expected from the equality of its ionic radius with that of Rb', and plays a role in defining possible NH, reorien-tatiom21 In the particular case of the insertion of ammonium into a lamellar host, the environment is clearly anisotropic. Vibrational Spectrum of the Tetramethylammonium Ion In the tetramethylammonium ion (TMA), skeletal C-N vibrations correspond to those of N-H in NHZ, such that for a tetrahedral arrangement only the antisymmetric N,C stretching and bending modes are expected in IR, both symmetric and antisymmetric being allowed in Raman.Of course, additional complexity is conferred upon the vibrational spectrum by the presence of the methyl groups. The appearance of their internal vibrations at characteristic positions nevertheless allows their identification, and the spectrum of TMA halides, for example, has been fully assigned in both Raman22 and IR23 spectroscopies. As expected, tor- sional modes of the methyl groups give considerable intensity in the neutron spectrum of TMA salts, which formed the subject of early studies using INS.24 A recent high-resolution INS spectrum of tetramethylammonium iodide, recorded on TFXA, has enabled a re-analy~is~~ of the detailed assignments of the published optical spectrum, and interpretations in the present paper will be based on this reassignment.a-Sn(HPO,), H20 Use will be made of detailed IR and Raman assignments of phosphate vibrations made on crystalline zirconium hydrogen ph~sphate,'~in conjunction with our previous INS data on SnP.', Results and Discussion Ammonium-exchanged Tin Hydrogen Phosphate INS, IR and Raman spectra of the intercalation compound SnP-NH, are reproduced in Fig. 1 and 2, with those of the SnP host (IR, Raman) for comparison. Spectral data and their assignments are detailed in Table 1 of the Supplementary Material.? (The band patterns of the IR and Raman spectra of SnP-NH, produced directly by reaction with ammonia vapour or by reaction of SnP or its allylammonium precursor with NH40H solution, are identical.) The IR spectrum of SnP and its ion-exchanged or interca- lated derivatives are dominated by a broad absorption culmin- ating in the range 1040-1100cm-', and resulting from vibrations of the PO4 tetrahedron, while P-OH stretching modes give strong bands at slightly lower wavenumber.In the present case, IR absorptions at 924 and 958 cm-' in the spectrum of SnP are absent after ion exchange, and a series of Raman lines at 961, 985 and 1047 cm- ' are replaced by a single band at 1017 cm- ', implying complete exchange of protons by ammonium. The same phenomenon is observed on ammonium exchange in U-Z~(HPO,)~H20.26 Lower- frequency manifestations of the PO4 group in Raman occur at 540 and 620 cm-' (v,) and 440cm-' (v2), (540, 626 and 420cm-' in IR), with rotation giving rise to a strong line at 350 cm-', slightly higher than that observed for ZrP.13 The triply degenerate bending mode v, of intercalated ammonium produces strong absorption in IR with two max- ima at 1404 and 1460 cm-', splitting indicative of a reduction in site symmetry from Td.Stronger evidence of symmetry lower than tetrahedral would be provided by the appearance t Supplementary data available (SUP 56861, 3 pages); details from Editorial Office. J. MATER. CHEM., 1991, VOL. 1 4000 3000 2000 1500 ' 1000 500 wavenumber/cm - (c) I I >. Y.- E.- v) v) Qc. .- Q c CI .- 1250 2050 2850 4050 wavenum ber/crn -' Fig.1 Infrared and Raman spectra of SnP and SnP-NH,. (a) IR spectrum of SnP 4000-400 cm- '; (b) IR spectrum of SnP-NH, 4000-400 cm-'; (c) Raman spectrum of SnP 2000-200 cm-'; (d) Raman spectrum of SnP-NH, 2000-200 cm-'; (e) mid-high-frequency Raman spectrum of SnP, showing vibrations of the OH group in IR of the formally forbidden v2 vibration, expected at ca. 1700 cm-'.A band of medium intensity is indeed observed at 1660 cm-', but its assignment to the scissoring vibration of co-intercalated water, c~~~~~~~~(H~O), displaced from its pos- ition in host SnP (1620cm-') to higher wavenumbers, must be preferred. The INS spectrum is useful in resolving any uncertainty in this assignment through the absence of sym- metry-based selection rules.Here, the maximum of greatest intensity in this spectral. region, at 1718 cm-', is absent in IR, and can thus be assigned to the doubly degenerate deformation, v,(NH,), and the shoulder at 1664 cm-',from Sscissor(H20), is also observed. The triply degenerate defor- mation vibration v4(NH4), is clearly seen at 1467 cm-' in INS. Stretching vibrations v1 and v3 of the ammonium ion are included in the broad absorption in IR between 2200 and 3700 cm-', with discernible maximum at 3160 cm-I, and low- and high-energy shoulders at 2840,3020 and 3475 cm -', respectively (weak scattering with maximum at 3105 cm-' in Raman). This range also covers the stretching vibrations of co-intercalated water, and the breadth and intensity in this region suggest the presence of strong hydrogen bonding.In the fully exchanged zirconium analogue, Zr(NH4P04)2 H20, for which single-crystal diffraction data are a~ailable,,~ the J. MATER. CHEM., 1991, VOL. 1 h g v) Fig. 2 INS spectrum of SnP-NH, 2000-30 cm-'. The vertical axis is proportional to S(Q,w)(arbitrary units) ammonium ions lie in cavities formed by oxygen atoms of the phosphate groups of two adjacent layers, and by that of a water molecule. Distances between nitrogen and oxygen atoms are as short as 2.72 A, indicative of strong hydrogen bonding2* and at least five oxygen atoms occur at hydrogen bonding distances, although no regular polyhedron is described. The spectroscopic data reported here are consistent with a similar crystal structure for SnP-NH, (although combined 15N and 31PNMR data2' seem incompatible with the pres- ence of NH,f-H20 hydrogen bonding), where retention of the tin phosphate layers, albeit of expanded interlayer spacing, is seen to be of greatest importance, such that no particular conformational adaptation to the insertion of NH, is made.Indeed, since oxygen atoms from two adjacent layers define the ammonium environment, it may be assumed that the rigidity of the individual sheets probably prevents any co- operative effect between layers. Under such conditions, it is not surprising that the site symmetry of NH4 is not strictly tetrahedral, since these ions must essentially occupy the site of minimal potential energy within the oxygen-atom cavities. To the high-energy side of the absorption envelope underly- ing the mid-frequency spectrum in IR, a series of weak features at 1860,2 100 and 2 180 cm -' may be assigned to combination bands, the first of which probably arises from the combination of v4 with the libration (rotation) vg.This mode, the position of which is indicative of the nature of interactions with the local environment, is unfortunately forbidden in optical spec- troscopy under strict Tdsymmetry. However, the appearance of the v4+v, combination was the criterion first suggested for the presence of hydrogen bonding in ammonium ~a1ts.l~ Combinations at similar positions have been observed in NH4SnF3, NH4C~S03,30 ammonium halides2' and in the anhydrous alum (NH4)2Pb(S04)2,31 where the ammonium ion lies in a similar environment between lead sulphate layers to that studied here.The difference (combination -fundamental) in each case indicates that v6 should occur at cu. 460 cm-'. Owing to a reduction in site symmetry, this mode could perhaps appear weakly, but the IR and Raman spectra are obscured in this region, even so, by vibrations of the PO4 group. More definitive information can be obtained from the INS spectrum, for which the same selection rules do not apply, requiring only that the vibration involves proton displacement for a detectable signal to occur. Here (Fig. 3) a broad, intense peak is observed, with maximum at 470cm-'. Its domination of the spectrum, and its occurrence in a region unoccupied in the spectrum of SnP, support its assignment as the rotational C .- u) .-$ E c 4000 3000 2000 wavenurnber/cm-' 1000 Fig.3 Vibrational spectra of SnP-TMA: (a) IR (b) INS (i) SnP- TMA. (ii) The INS data of tetramethylammonium iodide is repro- d~ced~~for comparison. Vertical axes are proportional to S(Q,o) (arbitrary units) mode of the ammonium ion. As expected, the position of this mode in INS between ammonium compounds is rather vari- able: 344cm-' in ammonium bromide,32a 440cm-' in ammonium tantalum tungsten reflecting, to a large extent, the strength of hydrogen-bond interactions of the ion with its immediate environment. The spectral regions below and above the 300-900cm-' librational mode domain are occupied by transitions resulting from whole-molecule vibrations, atom or ion translation, and internal vibrations, respectively.In the INS spectrum of SnP- NH4, a broad and poorly featured density of states is observed, with an intense shoulder at 137 cm-'. This has a counterpart in Raman at approximately the same position (147 cm-I), and could be assigned to the translational mode of NH,. Librational motion of co-intercalated water also gives rise to strong signals in INS in the 400-650 cm-' range, with the rocking and torsional modes observed (as shoulders) at 421 and 503 cm-', as in the spectrum of SnP.14 In this latter spectrum, the wagging mode, o(H20) was observed at 616 cm-', but in the present case, no distinct feature may be assigned to this mode which'may, however, be at least partially responsible for the tail to high-energy transfer between 550 and 700 cm-'.Finally, the absence of maxima at cu. 750 and ca. 1210 cm-l, resulting respectively from y and 6(POH)vibration^'^ provides spectral evidence for complete reaction with ammonia. J. MATER. CHEM., 1991, VOL. 1 Tetramethylammonium-exchangedTin Hydrogen Phosphate The spectral signature in IR (Fig. 3) indicating ion exchange of TMA for the layer protons is provided by the sharp, strong absorption at 950 cm- ' superimposed on the broad, intense band resulting from stretching vibrations of the phosphate group. Although its position is close to the P-OH stretching mode, seen as a shoulder at 965 cm-l, its intensity in IR and weakness in INS (at 944 cm-') justifies its assignment to the triply degenerate NC, stretch which has been observed at 951 cm-l in the IR af TMA iodide," and at 955 cm-' in the Raman spectrum of TMA-exchanged ~odalite.~~ The sym- metric skeletal mode is assigned to an intense line in the Raman spectrum at 757 cm-', but it is absent, as expected, from the IR.This mode is observed in the INS spectrum as a band of maximum at 740 cm- '. Skeletal deformations 6(NC4) have been assigned in the INS spectrum of TMA iodide (TMAI, Fig. 3) to features at 368 cm-' (6,) and 455 cm-' (aas),this latter superimposed on a phonon wing contribution arising from a methyl torsional mode at ca.350 cm-' (see below). Equivalent modes in the INS of TMAC1 have been identified at 371 (6,) and 456 (aa,) cm-1,34 the latter remaining unchanged for TMABr.34,35 In the neutron spectrum of SnP-TMA (Fig.3), peaks of similar shape and intensity may be observed at 374 and 458 cm-', only the latter being observed in the optical spec- trum (a weak Raman line at 457 cm-'). Combined vibrational data thus indicate that all skeletal modes (stretching and deformation) for inserted TMA occur at positions practically identical to those in crystalline TMAI (and other TMA halides), and it may be concluded that no chemical change or distortion of the TMA framework takes place. Strong Raman scattering at 960 and 989 cm- ', characteristic of P-OH vibrations, confirms the partial exchange of TMA for protons.The INS spectra of TMAI and SnP-TMA differ, however, in the positions of peaks attributable to methyl torsional vibrations. In the tetrahedral TMA group, the four methyl groups oscillate in two modes: a singly degenerate in-phase mode (a,) and a triply degenerate out-of-phase mode (fl). The former has been identified at 273 cm-' and the latter is split into its three components at 332,347 and 360 cm-' in TMAI. The variable position of the torsional modes in the series of TMA halides [265-301 cm-' (a,) and 344-370 cm-' (f1)25335] indicates their greater sensitivity to the crystal environment than the skeletal vibrations. It is not surprising to find more extensive shifts of the methyl torsional modes on insertion or occlusion of the TMA ion within an inorganic framework.In the present case, qn-phase is observed at 215 cm- ',whereas the triply degenerate mode gives an intense peak of maximum at 304 cm- ';this result agrees with recently reported INS spectra of TMA- inserted zeolites ZK4 and omega, where the in-phase torsions are observed at 245 and 206 cm- ',respectively, and the out- of-phase mode at 325 (TMA-ZK4) and 293 cm-' (TMA-omega).35 Closer structural similarity is expected with tri- methylammonium-inserted vermiculite, a phyllosilicate clay, and correspondingly the a, and f, modes differ little from those reported here, occurring at 230 and 294 cm-1.36 Indeed, these values tend to those calculated ab initio for the 'free' ion: 199 and 287 cm-', where the ion may be considered as in a cage of infinite dimension^.^^ Clearly the positions of both torsional modes are sensitive indicators of the interaction of TMA with its environment, and for all examples of inserted/ occluded TMA reported to date ion-host interactions are much weaker than TMA-C1, TMA-Br or even TMA-I.Of course, little or no hydrogen bonding is expected between this ion and the SnP host, unlike SnP-NH,. As in TMAI, the region above 470 cm- 'in INS contains broad bands expected to contain overtones and combinations of the torsional and skeletal modes, in addition to librational modes of co-interca- lated water, and possible deformation vibrations of any unex- changed POH.Correspondingly, and in agreement with our results on the SnP-NH, system, broad and intense bands are observed at 520, 626 cm-' [attributable to z and m(H,O)], and 750, 1190 cm-' [y, 6(POH)]. These assignments are detailed in Table 2 of the Supplementary Material. Conclusions We have shown in the present study that the combined use of optical (IR/Raman) and incoherent inelastic neutron scat- tering spectroscopies provides a powerful tool for the obten- tion of vibrational data on intercalated/ion-exchanged protonic species contained within an aprotic inorganic frame- work. In addition to species identification, such an inserted ion or molecule is a probe for the interlayer environment able to serve, for example, as an indicator of the strength of the host-guest interaction.Thus the site symmetry of ammonium ions strongly hydrogen bonded to the internal surface of the tin phosphate layers has been identified through IR/Raman activities, and its rotational mode was observed in INS. The absence of selection rules and the high sensitivity of INS for vibrational modes involving high-amplitude proton displace- ments makes this a particularly valuable method in the study of inserted methylammonium ions, where the methyl torsional vibrations give intense INS maxima. In contrast to the small, and strongly held ammonium ion in SnP-NH,, weak host- guest interactions occur in SnP-TMA, which are largely due to the absence of hydrogen bonding and, concomitantly, no evidence for any deformation of the relatively rigid tetrahedral NC, framework was seen.Swelling of a-tin phosphate by ion exchange of TMA is ca. 5 times that caused by intercalation of ammonium, and the layers may be considered as being 'propped apart' by the organic ions. As such, this vibrational spectroscopic study represents an approach to the structural and dynamical characterisation of pillared layered com-pounds. We thank Dr. C. Carlile and Mr. S. T. Robertson for per- mission to reproduce here the INS spectrum of TMAI prior to publication, and are grateful to SERC for access to neutron scattering facilities at ISIS. References A. Clearfield, Commun. Inorg. Chem., 1990, 10, 89. A. Clearfield, in Inorganic Ion Exchange Materials, ed.A. Clear-field, CRC Press, Boca Raton, 1982, ch. 2, pp. 75-106; G. Alberti, pp. 1-75 G. Alberti, M. Casciola, U. Costantino and M. Leonardi, in Solid State Protonic Conductors Ill for Fuel Cells and Sensors, ed. J. B. Goodenough, J. Jensen and A. Potier, Odense University Press, 1985; M. Casciola, U. Constantino and S. D'Amico, Solid State lonics, 1986, 22, 127; M. Casciola and D. Bianchi, Solid State lonics, 1985, 17, 287. A. Clearfield and G. D. Smith, Inorg. Chem., 1969, 8, 431; J. M. Troup and A. Clearfield, Inorg. Chem., 1977, 16, 3311; J. Albertsson, A. Oskarsson, R. Tellgren and J. 0. Thomas, J. Phys. Chem., 1971, 81, 1574. D. J. Jones and J. Roziere, XAFS VI; X-ray Absorption Fine Structure, ed. S. Hasnain, Ellis Horwood, Chichester, 1991, pp.405-407. U. Costantino, ch. 3, pp. 111-132 of ref. 2; M. Casciola, U. Costantino, L. Di Croce and F. Marmottini, J. lncl. Phenom. 1988, 6, 291. See, for example, A. Clearfield and R. M. Tindwa, J. lnorg. Nucl. Chem., 1979, 41, 871; S. Yamanaka, Y. Horibe, M. Tanaka, J. Inorg. Nucl. Chem., 1976, 38, 323. 928 J. MATER. CHEM., 1991, VOL. 1 A. Jimenez-Lopez, P. Maireles-Torres, P. Olivera-Pastor, E. Rodriguez-Castellon, M. J. Hudson and P. Sylvester, J. Zncl. Phenom. Mol. Rec. Chem., 1990,9 207. P. Olivera-Pastor, A. Jimenez-Lopez, E. Rodriguez-Castellon, A. A. G. Tomlinson and L. Alagna, J. Chem. Soc., Chem. Commun., 1989, 751; A. A. G. Tomlinson, in Pillared Layered 22 23 M. Pal, A. Agarwal, D. P. Khandelwal and H. D.Bist, J. Mol. Struct., 1984, 112, 309; G. Kabisch and M. Klose, J. Raman Spec., 1978, 7, 311; R. W. Berg, Spectrochim. Acta, 1978, MA, 655; M. Pal, G. S. Raghuvanshi and H. D. Bist, Chem. Phys. Lett., 1982, 92, 85. M. Stammler, J.Znorg. Nucl. Chern., 1967,29,2203; G. L. Bottger Structures: Current Trends and Applications, ed. I. V. Mitchell, Elsevier Applied Science, London, 1990, pp. 9 1-103; P. Maireles- Torres, P. Olivera-Pastor, E. Rodriguez-Castellon, A. Jimenez- 24 25 and A. L. Geddes, Spectrochim. Acta, 1965, 21, 1701. C. I. Ratcliffe and T. C. Waddington, J. Chem. SOC., 1976, 1935. J. Tomkinson, S. T. Robertson and C. Carlile, to be published. Lopez, L. Alagna, A. A. G. Tomlinson, J. Mater. Chem., 1991, 26 D. J. Jones, J. Roziere, J. Knowles and R.C. T. Slade, to be 10 1, 319. M. J. Hudson, E. Rodriguez-Castellon, P. Sylvester, A. Jimenez- 27 published. A. Clearfield and J. M. Troup, J. Phys. Chem., 1973,77, 243. Lopez and P. Olivera-Pastor, Hydrornetallurgy, 1990, 24, 77. 28 J. Emsley, Chem. SOC.Rev., 1980, 9, 91. 11 M. Casciola, U. Costantino, C. Paesini and R. Vivani, 5th Int. 29 M. J. Hudson and A. Workman, J. Mater. Chem., 1991, 1, 375. Conf. Solid State Protonic Conductors, Assisi, Sept. 1990; M. Casciola, S. Chieli and U. Constantino. 5th Int. Conf. Solid 30 0. Knop, W. J. Westerhaus and M. Falk, Can. J. Chem., 1980, 58, 270. State Protonic Conductors, Assisi, Sept. 1990. 31 I. A. Oxton, 0. Knop and M. Falk, Can. J. Chem., 1975, 53, 12 L. Basini, A. Rafaelli and G. Zerbi, Chem.Mater., 1990, 2, 679. 3394. 13 14 P. Colomban and A. Novak, J. Mol. Struct., 1989, 198, 277. D. J. Jones, J. Penfold, J. Tomkinson and J. Roziere, J. Mol. 32 (a) P. S. Goyal, J. Penfold and J. Tomkinson, Chem. Phys. Lett., 1986, 127, 483; (b) A. V. Powell and P. G. Dickens, Appl. Phys. Struct., 1989, 197, 113. A, 1990, 51,226. 15 16 U. Costantino and A. Gasparoni, J. Chromatogr., 1970, 51 289. G. Alberti, R. Bertrami, U. Costantino and J. P. Gupta, J. Znorg. 33 P. K. Dutta, B. Del Barco and D. C. Shieh, Chem. Phys. Lett., 1986, 127, 200. 17 Nucl. Chem., 1977, 39, 1057. P. S. Goyal, B. C. Boland, J. Penfold, A. D. Taylor and 34 C. G. Windsor, in Pulsed Neutron Scattering, Taylor and Francis, London, 1981, ch. 2. J. Tomkinson, in Dynamics of Molecular Crystals, ed. J. Lascombe, 35 T. 0. Brun, L. A. Curtiss, L. E. Iton, R. Kleb, J. M. Newsam, 18 Elsevier, Amsterdam, 1987, and references therein. J. P. Mathieu, C. R. Acad. Sci. Ser. C, 1955, 240, 2508. R. A. Beyerlein and D. E. W. Vaughan, J. Am. Chem. Soc., 1987, 109, 41 18. 19 T. C. Waddington, J. Chem. SOC., 1958,4340. 36 D. A. Neumann, Y.B. Fan, H. Kim, S. A. Solin, T. J. Pinnavaia 20 N. E. Schumaker and C. W. Garland, J. Chem. Phys., 1970, 53, and S. F. Trevino, National Institute of Standards and Technol- 21 392. D. J. Jones and J. Roziere, in Protonic Conductors: Solids, ogy, Summary of Activities July 1988 through June 1989. NIST Technical Note 1272, 1989. Membranes and Gels, ed. P. Colomban, Cambridge University Press, in the press. Paper 1/00995H; Received 4th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100923

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 929-933 Characterization and Photoelectrochemical Studies of CulnS, Thin Films Prepared by Sulphurization of Culn Alloy Akhlesh Gupta and A. Surya N. Murthy* Department of Chemistry, Indian Institute of Technology, New Delhi, 110 016, India Thin films of CulnS,, prepared by sulphurization of electroless deposited Culn alloy at different conversion temperatures and time durations, have been characterized by XRD and AES. The films converted at 250 and 350 "C are of mixed phase while those converted in the range 450-550 "C are of single-phase sphalerite with (112) as the preferred orientation. Detailed photoelectrochemical investigations show the best films are those obtained at a conversion temperature at 450 "C. Keywords: Thin Film ; CulnS,; Chalcogenide There is a considerable interest in ternary chalcogenide mater- ials, especially CuInS, and CuInSe, for use in photovoltaic devices.CuInSe, has been found to be promising in solid- state heteroj~nction'-~ and photoelectrochemical (PEC) The band gap of CuInS, (1.55 eV) is improved over that of CuInSe, (1.05 eV) and efficiencies of 9.7% have been reported using CuInS,-based PEC A variety of techniques have been used to prepare CuInS,"-l8 thin films, including a two-step technique involv- ing chalcogenation of CuIn alloy with H2S at high tempera- ture~.'~-,~This technique is useful because of the ease with which the film composition can be controlled, thereby making it possible to optimize the optical and electrical properties.Recently, Gupta et have prepared CuInS, thin films by such a two-step technique, in which electrolytically deposited CuIn alloy films were annealed at only one temperature, uiz. 550 "C, for 30 min in an H2S atmosphere. In this paper we report the effects of conversion temperature and duration of treatment on the structural, compositional and PEC proper- ties of CuInS, films. Experimental The CuIn alloy films were prepared by an electroless technique on etched and cleaned Ti substrate~~~3,~ The sulphurization of CuIn alloy films was carried out in a conventional tubular furnace in flowing 100% H,S gas. Before sulphurization, all films were annealed in an N, atmosphere at 200 "C for 15 min; this was found to ensure a uniform composition in the bulk of material.23 Conversion temperatures in the range 250-650 "C were controlled using a Mesibus temperature controller (DTC-6004). The influence of annealing for different time periods was investigated at a constant temperature of 550 "C.Alloy films made from a solution containing molar ratios of In :Cu =1 (X-type) and 1.5 (Y-type) were employed for conversion. X-Ray diffraction (XRD) patterns, Auger Elec- tion spectroscopic (AES) data and PEC data were obtained as described in ref. 23. X-Ray photoelectron spectra (XPS) were obtained on a Physical Electronics Inc., model PHI- 1800 employing Mg-KE radiation (E = 1253.6 eV). Trans- mission electron diffraction (TED) measurements were carried out using a TEM Model-JEOL JEM 200CX system.The PEC cell was illuminated with a 650 W tungsten- halogen lamp and the intensity of water-filtered light (80 mW ern-,) falling on the glass window was measured by a calibrated thermopile (Kipp and Zonan, CAI-754323, Hol- land). No correction was made for light absorption by electro- lyte and reflection by photoanode. Results and Discussion XRD patterns of CuInS, films obtained from X-type CuIn alloy films (Fig. 1) show that considerable amounts of impurity phases such as Cu,S, Ins, In2S3 or In,03 are present, but the major phase is undoubtedly CuInS,. The amount of impurity phases is larger in films converted at 250 "C than at 350 "C. The occurrence of Cu,S and In2S3 impurity phases decreases with increasing conversion temperature. At higher temperatures, an increasing amount of CuInS, is formed directly from the metal alloy and also indirectly uia inter-diffusion of the binary sulphides.It is interesting that the formation of single-phase material was reported at a conver- sion temperature of 250 "C by Binsma and van der Linden" and at 350 "C by Grindle et aL20 with annealing times of 2 h in each case. Our films prepared at 350 "C (2 h) still contain impurity phases. We observed single-phase CuInS, when the conversion was carried out at 550 "C for 15 min. A single-phase, polycrystalline, sphalerite film with (112) as the pre- ferred orientation could also be obtained when a conversion temperature of 450 "C was applied for 30 min [Fig.l(c)]. The sphalerite structure has been reported for CUI~S,'~*~~ films prepared by the two-step technique. Hodes et al.," however, reported a chalcopyrite structure for CuInS, and conjectured that the high conversion temperature (550 "C) is responsible for such a structure, but our films that were converted at the same temperature and for the same duration are found still to possess the sphalerite structure [Fig. l(d)]. Attempts to convert the sphalerite CuInS, films into the chalcopyrite phase by an additional annealing" at 400 "C for 120 min in N, was unsuccessful. However, the crystalline properties of the film improved, as evidenced by the sharpness of the major diffraction peaks. While the films converted at 550 "C were of single phase [Fig.l(d)], the XRD pattern of the film obtained at 650 "C [Fig. l(e)] show some extra peaks characteristic of Ins impurity phase and of a compound containing Ti and S [Fig. l(f)], along with CuInS, peaks. A comparison of Fig. l(c) and (d) shows that the structure and orientation of the films converted at 450 and 500°C are the same, thus establishing that the crystalline structure is relatively insensi- tive to the conversion temperature in the range 450-550 "C and Cu, In and S form a single phase and stoichiometric CuInS, films. In order to confirm the nature of the phases and to detect any impurity phases, TED measurements were performed. The TED pattern of CuInSz films converted from X- and Y-type CuIn alloy are shown in Fig.2. The d-values, calculated from the diameter of rings in the TED patterns, b I 0 0 0I I.(c)I I I I 0 0 20 40 60 80 20 40 60 80 201° 2el" Fig. 1 XRD patterns of CuInS, films, converted at (a)250, (b)350, (c) 450, (d) 550, (e)650 "C and (f)Ti substrate annealed at 650 "C in H,S. Cu,S; .,0,CuInS,; 0,Ti; x, Ins; 0, (Ti-S); A, In,S,; A,In,O, (a) Fig. 2 TED patterns of CuInS, films from (a)X-type and (b) Y-type,CuIn alloy (see text) are compared with XRD data and standard d-values in Table 1. The data are consistent with the formation of polycrystalline CuInS,. The characteristic d-values for the chalcopyrite. phase and other impurity phases are absent. The TED and XRD patterns23 therefore confirm the forina- Table 1 Comparison of TED and XRD data calculated" dlA hkl XRDb 3.16 112 3.17 3.04 103 - 2.74 200,004 2.75 2.39 21 1 - 2.04 2 13,105 - 1.94 220,204 1.95 1.66 312,116 1.66 1.59 224 1.59 1.37 400,008 1.38 1.26 3 16,332 1.26 1.23 404 - 1.13 228 1.13 "Ref.35. bData from Fig. l(c). 'Data Fig. 2(b). observed, d/!i TED' TEDd 3.16 3.17 - - 2.74 2.74 - - - - 1.94 1.95 1.67 1.67 1.60 1.60 1.39 1.39 1.26 1.28 - - 1.13 1.13 from Fig. 2(a). dData from tion of a single-phase, polycrystalline thin film with the sphalerite structure. AES analysis shows that oxygen, if present, is <5 atom% in all samples, irrespective of the conversion temperature, and the proportion of sulphur on the surface remains uniform. The Cu:In ratio (1.34) at the surface of the film converted at 250 "C progressively decreased towards unity with increasing temperature, the proportion of indium increasing correspond- ingly.This implies that indium loss (probably as In2& seen as the yellow deposition in the cold region of the tube) is greater at low temperatures and decreases with increasing conversion temperature. This, may be due to the fact that at lower temperatures the rate of In loss as In2& is greater than the rate of CuIn alloy conversion to CUI~S~.~' Depth profile J. MATER. CHEM., 1991, VOL. 1 analyses of the film (Fig. 3) show that the films converted at 250 and 350 "C are non-uniform in the bulk in terms of their Cu :In ratio.Increasing the conversion temperature causes the ratio to become more uniform. It was thought that besides annealing temperature annealing duration is also important. Therefore, the films were converted at 550 "C for varying times of 15, 30 and 60 min. The XRD patterns show that all the films are of a single phase with the sphalerite structure. AES analysis of these films at the surface and in the bulk show that conversion duration does not have a marked effect and all the films are almost of the same composition and uniformity in depth. It can be concluded that CuIn alloy can be completely converted into CuInS, using 550 "C conversion for 15 min or conversion at 450 "C for 30 min. XPS of single-phase CuInS, was carried out in order to determine the valence states of Cu and In and their binding energies.The observed binding energies of Cu 2p3 /2, Cu 2p, /2, In 3d,,,, In 3d3,, and S 2p are in good agreement with those reported in the literature (Table 2) for single-phase CuInS, thin films. Since the binding energies for Cu and In in impurity phases (such as Cu2S, In203, In2S3) are very close to those of Cu and In in CuInS,, it is very difficult to establish the absence of impurity phases in CuInS,. However, some peak broadening is expected if impurity phases are present. The full-width at half-maxima (FWHM) calculated for Cu 2p3 /2, In 3d,/, and S 2p for CuInS2 film are in good agreement with literature values (Table 2). The difference in binding energy of Cu 2p3/, and S 2p [A(Cu-S)]; In 3d5,, and S 2p [A(In-S)] are also in agreement with the literature values (Table 2). These results indicate that CuInS, films converted 100 I 60ti 20 .-c 60 a 401 0 O/ 801:,1--------;20 0 0 6 12 18 sputter tirnelrnin Fig.3 AES depth profile of CuInS, film converted at (a)250, (b)350 and (c) 450 "C 93 1 Table2 Binding energies (in eV) for Cu, In and S associated with CuInS, E,IeV thin thin film in film film present thin single (single (impure thin XPS study film" crystal" phase)b phase)b film' Cu 2p,,, 952.3 -951.87 952.5 953.0 -CU 2p3,, 932.3 930.8 931.7 932.7 933.2 932.6 (1.9) (2.5) (1.9) (1.8) (2.3)In 3d,,, 452.1 -452.7 452.3 452.3 451.9 In 3d,,, 444.4 443.4 444.6 444.7 444.6 444.3 (1.4) (2.4) (1.4) (2.1)s 2P 161.7 -161.5 161.8 161.8 -(2.1) (2.4)A(Cu-S) 770.6 -770.2 770.9 771.4 -A(1n-S) 282.7 -283.2 282.9 282.8 -A(Cu-S), Binding energy difference between Cu 2p3,, and S 2p peaks.A(1n-S), Binding energy difference between In 3d,,, and S 2p peaks. Values in parentheses represent the FWHM. "Ref. 26. bRef. 27. 'Ref. 28. at 450°C for 30 min do not have any impurity phases like Cu,S or In,03. Detailed PEC studies on all films have been carried out in polysulphide solution. The stoichiometric CuInS, films (from X-type CuIn alloy) were p-type, showing negligible photo- voltaic activity, while the other films that contained an excess of In were n-type and showed good photovoltaic activity.This is as expected since the n-type CuInS, materials, includ- ing the single crystal29 show more band bending than p-type materials in any redox Therefore, detailed PEC experiments were carried out only for CuInS, films obtained from Y-type CuIn alloy films. The dark and photo I-V characteristics of CuInS, film converted at 450 "C for 30 min are shown in Fig. 4.The short- circuit current (SCC) variation is in the range 8.5-10 mA cm-2 14 f 8 a 6E 2 4 2 ,I I /-.'I I 1 +200 +400 V/mV Fig. 4 Current-voltage characteristics of CuInS, film electrode in polysulphide (3 mol dmP3 NaOH, 3 mol dm-3 Na,S and 4 mol dm-3 S) in the dark and under illumination of 80 mW cm-, 932 J.MATER. CHEM., 1991,VOL. 1 for different batches of samples, and the open-circuit voltage 60 - (V0J remains almost the same (ca. 340 mV). A steep rise in the dark anodic current at a reverse bias of ca. +0.25 V is typical of these films and limits our ability to measure photocurrent where there is strong band bending. From the 50 - photocurrent onset measurements a flat-band potential (Efb) of -0.45 V was obtained. This is larger than Efbfor electro- plated CUI~S,,'~ but it is comparable to that obtained with ~40c .- slurry-painted CUI~S,~' and by sulphurization of electro- C 3 plated CuIn alloy.21 The fill factor is small (0.22),typical of the n-CuInX,/polysulphide ~y~tem,~,~~*~~*~~ and is not neces- n5 30 sarily indicative of the film quality.The spectral response of the cell is shown in Fig. 5. More notable is the almost flat response between short-wavelength absorption of the electro- lyte and the long-wavelength semiconductor absorption edge; all samples gave a similar shape. Some sub-bandgap response was also observed, which may be due to excess of In (excess of In was confirmed by AES analysis but not detected in the XRD pattern).23 The formation of In-S or In-0 compound or CuIn,S8 is a po~sibility'~*~~ and is indicative of the intrinsic defect state in the material, giving rise to optical transitions when the illumination intensity is less than the bandgap energy.33 The extrapolation of the linear portion of (4,h~)~ us. hv plot (Fig. 6) gave the value of the bandgap, 1.44 eV, which is in good agreement with the values of 1.46eV,,' 1.43 V,34 1.45 eVI8 and 1.44 eV', for CuInS, thin films but smaller than that for the single crystal 1.5 eV,35 1.48 eV8 and 601 50.00" g @ \€30-/-g 20 -10 0' I I I I I N h>c:2 20 ' 10. I I 1.3 1.4 1.5 1.6 hvleV Fig. 6 (4,hv)' us. hv for the determination of the bandgap calculated value of 1.55 eV. This difference may be due to sub-bandgap defects. A detailed PEC study of CuInS, films prepared under different conditions has been carried out in polysulphide electrolyte and data are presented in Table 3. The PEC characteristics of the film obtained at 450 "C are better than those for the film obtained by electrodeposition" or screen printing3' and are comparable to the film obtained by sulphurization of electroplated CuIn all~y.'~,~~**~ The PEC characteristics of the film begin to deteriorate as the conver- sion temperature increases above 450 "C, although there was not much deterioration between 450 and 550 "C.When the conversion temperature was 650"C, the PEC response was very poor, possibly due to the presence of impurity phases (Ins and Ti-S). The effect of conversion duration (15, 30 and 60 min) on the PEC properties was also studied, the films converted response curves the the same for all samples shapeof spectral for 30 min gave was best performance. The except that converted at 650 "C. Two values of the bandgap energy were calculated for this sample from its spectral response curve. The stability of the film (Y-type alloy converted at 450 "C for 30 min) has been examined in polysulphide electrolyte at short-circuit current (SCC) and maximum power point (Fig.7).The current initially increases at both points. Since an Table 3 Photoelectrochemical data on CuInSz (from Y-type CuIn alloy) converted under different conditions current conversion temperature/ "C, durationlmin light intensity /mW cm-2 density (J =ISCIA) ImA cm-2 open-circuit voltage, vo,/mv fill factor efficiency("/.I flat-band potential" E,,ImV bandgap energy /eV 450, 30 550,30 80 80 9.87 6.80 335 380 0.22 0.22 0.90 0.73 380 440 1.44 1.45 650, 30 80 1.33 350 0.29 0.17 400 1.41 and 1.33 550,15 550,60 80 80 5.83 4.23 350 340 0.22 0.21 0.50 0.38 370 380 1.44 1.43 "Potential against the solution potential. J.MATER. CHEM., 1991, VOL. 1 c 0 4 8 12 16 tih Fig. 7 Stability of n-CuInS, (obtained from Y-type alloy) converted at 450 "C for 30 min at (a)the short-circuit point and (b)the maximum power point current is observed at the SCC point. Such a fall in current has been observed for thin film~~l,~~and for the single crystaLZ9 However, at the maximum power point, the current is stable [Fig. 7(b)]. Therefore, the operation of a cell at maximum power point is more advantageous than at the SCC point. Conclusion (1) Deposition by the electroless method is as good as elec- trodeposition for the preparation of CuInS, films.(2) XRD, TED and XPS analyses confirm the presence of single-phase, (1 12) oriented, sphalerite structure of CuInS, films obtained at 450 "C. (3) Films converted at low or very high temperature contain impurity phases. (4) The compositional uniformity of films increases with temperature. (5) Films obtained at 450 "C are better suited for PEC cells. (6) Long-term operation is advantageous at the maximum power point rather than at the short-circuit point. The financial support of the Department of Non-conventional Energy Sources (no. 2/5/4/82 and 102/6/86/NT) Government of India, and IIT is gratefully acknowledged. The authors thank Dr. G. K. Padam, National Physical Laboratory, New Delhi, and Dr. S. P. Singh, Department of Physics, IIT Delhi, for helpful discussions.References 1 W. E. Devaney, R. A. Mickelsen and W. S. Chen, in Proc. 10th IEEE Photovoltaic Specialists Conf., Las Vegas, 198.5, New York, 1986, p. 1733. 2 R. Noufi, R. J. Matson, R. C. Powell and C. Herrington, Solar Cells, 1986, 16, 479. 3 R. A. Mickelson, Proc. Polycryst. Thin Film Review Meeting, 1983, Golden, SERI Publication CP211- 1985. 4 G. Razzini, L. P. Bicelli, B. Scrosati and L. Zanotti, J. Electro-chem. SOC., 1986, 133, 351. 5 D. Cahen and Y. W. Chen, Appl. Phys. Lett., 1984,46, 746. 6 D. Haneman and J. Szot, Appl. Phys. Lett., 1985, 46, 778. 7 S. Menezes, Appl. Phys. Lett., 1984, 45, 148. 8 M. A. Russak and C. Carter, J. Electrochem. SOC., 1985, 132, 1741. 9 J.G. Fleming, M. L. Feaheiley and H. J. Lewerenz, J. Electro-chem. SOC., 1989, 136, 1506. 10 H. J. Lewerenz, H. Goslowsky, K. D. Husemann and S. Fiechter, Nature (London), 1986, 321, 687. 11 L. L. Kazmerski, M. S. Ayyagari and G. A. Sanborn, J. Appl. Phys., 1975, 46, 4865. 12 H. L. Hwang, C. C. Tu, J. S. Maa and C. Y. Sun, Solar Energy Mater., 1980, 2, 433. 13 H. L. Hwang, C. L. Cheng, L. M. Liu and C. Y. Sun, Thin Solid Films, 1980, 67, 83. 14 H. L. Hwang, B. H. Tseng, C. Y. Sun and J. J. Loferski, Solar Energy Muter., 1980, 4, 67. 15 P. Rajaram, R. Thangaraj, A. K. Sharma, A. Raza and 0. P. Agnihotri, Thin Solid Films, 1983, 100, 111. 16 G. K. Padam and S. U. M. Rao, Solar Energy Muter., 1986, 13, 297. 17 A. N. Tiwari, D. K.Pandya and K. L. Chopra, Thin Solid Films, 1985, 130, 217. 18 R. N. Bhattacharya, D. Cahen and G. Hodes, Solar Energy Muter., 1984, 10, 41. 19 J. J. M. Binsma and H. A. Van Der Linden, Thin Solid Films, 1982, 97, 237. 20 S. P. Grindle, C. W. Smith and S. D. Mittleman, Appl. Phys. Lett., 1979, 35, 24. 21 G. Hodes, T. Engelhard, D. Cahen, L. L. Kazmerski and C. R. Herrington, Thin Solid Films, 1985, 128, 93. 22 G. Hodes and D. Cahen, Solar Cells, 1986, 16, 245. 23 A. Gupta, A. N. Tiwari and A. S. N. Murthy, Solar Energy Muter., 1988, 18, 1. 24 A. Gupta and A. S. N. Murthy, J. Muter. Sci. Lett., 1989,8, 559. 25 C. D. Lokhande and G. Hodes, Solar Cells, 1987, 21, 215. 26 Y. Mirovsky, R. Tenne, D. Cahen, G. Swatzky and M. Polak, J. Electrochem. SOC., 1985, 132, 1070. 27 A. N. Tiwari, Ph.D. Thesis, Indian Institute of Technology, Delhi, 1986. 28 P. Rajaram, R. Thangaraj, A. K. Sharma and 0. P. Agnihotri, Solar Cells, 1985, 14, 123. 29 Y. Mirovsky, D. Cahen, G. Hodes, R. Tenne and W. Giriat, Solar Energy Muter., 1981, 4, 169. 30 G. Hodes, T. Engelhard, J. A. Turner and D. Cahen, Solar Energy Muter., 1985, 12, 211. 31 Y. Mirovsky and D. Cahen, Appl. Phys. Lett., 1982, 40, 727. 32 F. A. Theil, J. Electrochem. Soc., 1982, 129, 1570. 33 R. Haak, D. Tench and M. A. Russak, J. Electrochem. SOC., 1984, 131, 2709. 34 M. Gorska, R. Beaulieu, J. J. Loferski and B. Roessler, Solar Engery Muter., 1979, 1, 313. 35 A. Venkatarathnam and G. V. Subba Rao, Muter. Chem. Phys., 1987, 16, 145. 36 L. L. Kazmerski, M. A. Ayyagari, G. A. Sanborn, F. R. White and A. J. Merrill, Thin Solid Films, 1976, 37, 323. 37 C. D. Lokhande, J. Power Sources, 1987, 21, 59. Paper 1/O 12641; Received 18th March, 199 1

ISSN:0959-9428    

DOI:10.1039/JM9910100929

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 935-938 Preparation and Characterization of wholly Aromatic para-Linked Copolyamides of Poly(p-phenyleneterephthalamide) Kazuki Suehiro,* Takayuki Tsutsumi, Miyuki Kuramori and Kunio Ide Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga, 840 Japan Wholly aromatic para-linked copolyamides of poly( p-phenyleneterephthalamide) have been prepared by direct polycondensation via a phosphorylation reaction using various amounts of p-aminobenzoic acid, toluene-p- diamine or nitroterephthalic acid (NTA) as comonomer. Viscosity number, perhaps degree of polymerization as well, increased with increasing comonomer content, whereas crystallinity of copolymers decreased. In particular, a bulky nitro group decreased crystallinity and the copolymers with NTA content >50 mol% were amorphous and similar to poly (p-pheneylenenitroterephthalamide). Melting point was not greatly changed by copolymeriz- ation.Thermal decomposition temperatures of copolymers containing NTA were lower than those of other copolymers by ca. 100 "C. Keywords: Copolymer; Viscosity ; Polyamide Poly(p-phenyleneterephthalamide)(PPTA) spun in the liquid- phate, terephthalic acid (TA), nitroterephthalic acid (NTA) crystalline state has high mechanical strength and is a high- and p-aminobenzoic acid (ABA), and examined the effect of tensile-modulus fibre. It also has a high melting point and comonomer structures on crystallinity and thermal properties good thermal stability.But PPTA is hard to process and has of copolymers. Note that ABA is a monomer of poly(p- poor solubility in organic solvents. Various methods have benzamide) (PBA), which is another wholly aromatic para- been tried in attempts to circumvent these limitations: intro- linked polyamide having excellent mechanical properties and duction of substituent groups onto the benzene rings,' N-sub- thermal stability. ~titution,~~~ etc. Copolymerization with cop~lymerization,~ meta-linked monomers increases the solubility and lowers the melting point, but the decomposition temperature and the crystallinity decrease^.^ In addition, mechanical properties of Experimentalmeta-linked aramids, such as poly(m-phenylene isophthalam- Materialside), are inferior to those of para-linked PPTA.Therefore, we prepared (Scheme 1) three types of wholly N-Methyl-2-pyrrolidone, pyridine and N,N-dimethylaceta-para-linked PPTA copolymers, with various compositions, mide were purified by vacuum distillation. Commercially from phenylene-p-diamine (PD), toluene-p-diamine (TD) sul- obtained anhydrous LiCl was dried at 130 "C for 24 h in -xH,NoNH2 + xH02COCO2H + (1-2x)HZN 0 C 0 2 H -*12NeNH2 + (1-x)H2NaNH2 + H02CeC02H H2NoNH2 + xH02CeCO2H + (1-4H02C-Scheme 1 (a) PD/TA/ABA copolymer; (b)(PD/TD)-TA copolymer; (c) PD-(TA/NTA) copolymer uucuo. All other chemicals were reagent grade and were used as received. Polymerization Aromatic polyamides, for example PPTA, are usually prepared by the low-temperature solution reaction between tereph- thaloyl chloride and phenylene-p-diamine in amide solvents such as hexamethylphosphoric triamide and N-methyl-2-pyr- rolidone.6 In the present study, we employed a more con- venient direct polycondensation method developed by Yamazaki and Higashi in which the carboxylic groups need not be chlorinated prior to p~lymerization.~ Thus, 20 mmol of monomers were heated at 100-105 "C for 3 h under nitro- gen in a mixed solvent of N-methyl-2-pyrrolidone (50 cm3) and pyridine (10 cm3) containing triphenyl phosphite (22 mmol) and LiCl (2.0g).After it had been cooled, the reaction mixture was poured into methanol and the precipitate was washed with water and then methanol, followed by vacuum drying.Measurements Viscosity numbers (q,,/C where qsp=specific viscosity and C =concentration) were measured with an Ostwald viscometer at 30 "C using a 5 g dm-3 solution in concentrated sulphuric acid. Thermogravimetric and differential thermal analyses were done at a heating rate of 10 "C min-' in a nitrogen atmosphere. X-Ray diffraction patterns were obtained with graphite-monochromatized Cu-Ka radiation. Solubility of polymers was observed in N,N-dimethylacetamide containing 5% LiCl at room temperature. Results and Discussion Pale- to dark-yellow polymers were obtained in good yields of over 92% (Table 1). Viscosity numbers of the copolymers in concentrated sulphuric acid solution were generally higher than those of the homopolymers of the constituent Table 1 Effects of composition on characteristics of PPTA cop01 yamides composition yield (%p/C)/ (Oh)(mol%) lo-' dm3 g-' T,"/ "C Tdb/"C (a) PD/TA/ABA copolymers PD/TA/ABA 50/50/0 100 0.48 517 499 40/40/20 100 0.79 525 51 1 30/30/40 20/20/60 100 98 2.24 4.13 530 525 506 515 10/10/80o/o/ loo 97 98 2.70 1.72 522 525 522 485 (b)(PD/TD)-TA copolymers PD/TD 100/0 100 80120 93 0.48 1.27 517 500 499 499 60140 95 1.63 500 494 40160 94 4.80 515 520 20180 93 2.93 510 516 0/100 92 0.93 515 504 (c) Pd-(TA/NTA) copolymers TA/NTAI 0010 100 0.48 517 499 75/25 50150 96 95 1.47 6.19 512 - 443 424 25/75 01100 95 95 5.09 3.52 414 403 " Melting point; temperature of 10% weight loss.J. MATER. CHEM., 1991, VOL. 1 comonomers in the copolymers. All copolymers rich in PPTA content had rather low viscosities. Highly crystalline PPTA had the lowest viscosities, whereas amorphous PD- (TA/NTA) copolymers had especially high viscosities. These copolymers are less crystalline as will be shown later and would be more soluble in the solvent during the polymeriz- ation process, possibly making the chain-growth reaction easier to achieve. All homopolymers and copolymers prepared were soluble in sulphuric acid. The amorphous PD-(TA/NTA) copolymers comprised of more than 50mol% NTA dissolved in N,N-dimethylacetamide containing 5 wt.% LiCI. PBA and poly(me- thyl-p-phenylene terephthalamide) (PMPTA) were also soluble in it, but PPTA and other crystalline copolymers were insol- uble or partially soluble.When a sulphuric acid solution of polymers was smeared on a glass plate and coagulated by soaking in water, thin films could be obtained for all polymers with viscosities higher than 0.127 dm3 g-'. X-Ray diffraction curves of copolymers and corresponding blends are shown in Fig. 1-5. A comparison of Fig. 1 and 3 10 20 30 201° Fig. 1 X-Ray diffraction curves of PD/TA/ABA copolymers PPTA/PBA (PD/TA/ABA) (50/50/0) *.-I89 (10/10/80) 10 20 30 20t0 Fig. 2 X-Ray diffraction curves of blends of poly(p-phenylene tereph- thalamide) (PPTA) and poly( p-benzamide) (PBA) J. MATER. CHEM., 1991, VOL. 1 /fi \oo/o (PPTA) 780120 .-/\ iiz_i; \-o/loo(PMPTA) I I I I 10 20 30 261" Fig.3 X-Ray diffraction curves of (PD/TD)-TA copolymers PPTA /PMPTA (mol %) 10 20 30 26i" Fig. 4 X-Ray diffraction curves of blends of poly(p-phenylene tereph- thalamide) (PPTA) and poly(methy1-p-phenylene terephthalamide) (PM PTA) with Fig. 2 and 4,respectively, shows that crystallinities of these copolymers are apparently lower than those of the homopolymer blends with the corresponding comonomer compositions. Therefore, the copolymerization reaction would appear to proceed practically at random. Since bulky nitro groups on the phenyl rings hinder crystallization, the PD- (TA/NTA) copolymers whose NTA content is more than 50mol% are amorphous. On the other hand, since a methyl group is not as bulky as a nitro group, the (PD/TD)-TA copolymers are somewhat crystalline.The X-ray diffraction patterns of the PD/TA/ABA and (PD/TD)-TA copolymers changed gradually with increasing content of another comono- mer. Consequently, the crystal structures of these copolymers would also undergo a gradual change. A minor comonomer TA/NTA 10 20 30 261" Fig. 5 X-Ray diffraction curves of PD-(TA/NTA) copolymers sequence might be relatively easily excluded from the crystal of the major component in the case of a copolymer composed of a flexible chain such as an aliphatic copolyamide. In contrast, rejection of the rigid comonomer unit is difficult in the course of crystallization of the wholly aromatic para- linked copolyamides and the resulting crystal has the charac- teristics of a mixed crystal.Although melting points of the PD/TA/ABA copolymers were slightly higher than those of the (PD/TD)-TA copoly- mers with pendant methyl groups, the melting points of these copolymers were in the vicinity of 500 "C which is similar to those of PPTA and other homopolymers (Table 1). Lowering of the melting points is usually observed for aliphatic copoly- amide~.*.~However, the present aromatic copolyamides did not show a distinct melting-point depression, eutectic behav- iour. This is because, as previously mentioned, the crystal structures of the copolymers are gradually transformed from that of one homopolymer to that of another with the change in the comonomer composition, namely, having an isomorph- ous tendency.The temperatures of the 10% weight loss for the original weights were used as a measure of thermal stability and are listed in Table 1. The corresponding temperatures of the crystalline copolymers are also only slightly affected by the composition similar to the melting points. The decomposition temperature of the amorphous PD-(TA/NTA) copolymers was nearly 400 "C and evidently lower than those of the crystalline copolymers. The 10% weight loss temperatures of terephthalic acid and nitroterephthalic acid were 3 13 and 269 "C, respectively. Therefore, low decomposition tempera- tures of poly(p-phenylene nitroterephthalamide) (PPNTA) and PD-(TA/NTA) copolymers are attributable to the thermal instability of nitroterephthalic acid.In conclusion, the crystallinity of PPTA decreases gradually but the melting point and decomposition temperature are not changed markedly by the copolymerization with ABA or TD. However, NTA having a bulky nitro group decreases the crystallinity significantly and lowers the thermal stability. References 1 R. Takatsuka, K. Uno, F. Toda and Y. Iwakura, J. Polym. Sci., Polym. Chem. Ed., 1977, 15, 1905. 2 M. Takayanagi and T. Katayose, J. Polym. Sci.,Polym. Chem. Ed., 1981, 19, 1133. 938 J. MATER. CHEM., 1991, VOL. 1 3 4 5 6 M. Takayanagi and T. Katayose, J. Polym. Sci., Polym. Chem. Ed., 1983, 21, 31. Y. Imai, N. Hamaoka and M. Kakimoto, J. Polym. Sci., Polym. Chem. Ed., 1984, 22, 1291. T. Kiyotsukuri and K.Tsujimoto, Sen-i Gakkaishi (J. SOC.Fiber Sci. Tech. Jpn.), 1978, 35, T-13. T. I. Bair, P. W. Morgan and F. L. Killian, Macromolecules, 1977, 10, 1396. 7 8 9 N. Yamazaki, M. Matsumoto and F. Higashi, J. Polym. Sci., Polym. Chem. Ed., 1975, 13, 1373. W. Mokudai, M. Ishihara, C. Morishita and R. Oda, Rikagaku-kenkyusho Iho (Bull. Inst. Phys. Chem. Res.), 1940, 19, 1448. K. Suehiro, T. Egashira, K. Imamura and Y. Nagano, Acta Polym., 1989, 40,4. Paper 1/01526E;Received 2nd April, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100935

出版商:RSC    

年代:1991

数据来源: RSC