ISSN:0959-9428    

DOI:10.1039/JM99505FX001

出版商:RSC    

年代:1995

数据来源: RSC

ISSN:0959-9428    

DOI:10.1039/JM99505BX003

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Cumulative Author Index 1995 Alario-Franco M.A., 195 Chung H. M., 71 Anderson J. E., 13 Clearfield A., 171 Archer L. B., 151 Cole-Hamilton D. J., 47 Armelao L., 79 Cook S. L., 47 BaEakova L., 27 Cordoncillo E., 85 Badenes J., 85 Crociani L., 79 Bae M.-K., 71 Darriet B., 165 BaAares Mufioz M. A., Depaoli G., 79 Dickens P. G., 141 Battle P. D., 75 Dragone R., 183 Baudy-Floc’h M., 35 Eastmond G.C., 195 Becker J.Y., 191 Escribano P., 85 Benitez J. J., 175 Flynn G. J., 141 Bertoncello R., 79 Forder S., 97 Bettinelli M., 79 Frank C. W., 13 Bhardwaj C., 171 Fu X., 109 Bosch P., 175 Gay D. H., 133 Breen C., 97 Gazzoli D., 183 Brooks J. S., 97 George A. R., 133 Bryce M.R., 191 Gherardi M., 183 Capitiin M. J., 175 Gibb T.C., 75, 91 Carda J., 85 Gilliland D. D., 47 Carrizosa I., 175 Goldenberg L.M., 191 Centeno M. A,, 175 Goodby J. W., 1 Chandlcr C. D., 151 Granozzi G., 79 Chippindale A. M., 141 Gravereau P., 165 Choy J.-H., 57, 65 Guillemet M., 35 Ha Y. S., 71 Lisa V., 27 Poojary D. M., 171 Hampden-Smith M. J., 151 Locke W., 159 Raoul J. M., 35 Han Y.-S., 57, 65 Lopez Gonzalez Robert A., 35 Harris K. D. M., 133 J. d. D., 127 Rohl A. L., 133 Hasegawa I., 193 Maggs A. A., 97 Rybka V., 27 Hayashi H., 115 Malet P., 175 Sawa H., 41 Herod A. J., 75, 91 Marshall G., 97 Seed A. J., 1 Hitchman M. L., 47 Matsubayashi G.-e., 105 Sergeev G., 31 Hnatowicz V., 27 McDonnell D. G., 1 Shamlian S. H., 47 Hodges J. P., 75 Melghit K., 147 Snowden M.J., 195 Hoffmann D.A,, 13 Minelli G., 183 Stephenson G. R., 97 Hosokoshi Y., 41 Mitchell P. C. H., 159 Sterte J., 121 Hou W., 109 Monros G., 85 Stuttard G. P., 141 Huang P.-n., 53 Motojima S., 193 Sundholm F., 195 Hudson M. J., 115, 159 Mun M.-O., 71 SvorEik V., 27 Kajiwara M., 193 Nakajima H., 105 Tamura M., 41 Kato R., 41 Nakamura T., 193 Tena M. A., 85 Khodorkovsky Yu., 191 Nash J. A. P., 47 Thompson S. C., 47 Kim J.-T., 57, 65 Odriozola J. A,, 175 Tondello E., 79 Kim Y.-H., 57 Otterstedt J.-E., 121 Torncrona A., 121 Kingsborough R., 151 Park Y. W., 71 Touboul M., 147 Kinoshita M., 41 Pelle F., 35 Toyne K. J., 1 Kocourek F., 27 Peng B., 109 Valigi M., 183 Lambert J.-F., 165 Peng N., 91 Vicente Rodriguez Launay J.-C., 165 Petric A,, 53 M.A., 127 Lee S., 71 Petrukhina M., 31 Yan Q., 109 Lee S.-I., 71 Petty M.C., 191 Zagorsky V., 31 i Conference Diary January 29-Advanced Solid-state Lasers February 1 Memphis, TN, USA Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC 20036, USA. Tel: +1 202 223 8130; Fax: +1202 416 6130. February 16 Radiation Curing and Processing of Materials London, UK SCI Conference Secretariat, 14/15 Belgrave Square, London, UK, SWlX 8PS. Tel: +44 171 235 3681; Fax:+44 171 823 1698. February 16-17 VIIIth Colloquium on Biomaterials Aachen, Germany Dr. H.A. Richter, Institute of Pathology, Technical University Aachen, PauwelsstraRe 30, 52074 Aachen, Germany. Tel: +49 241 80 89690; Fax: +49 241 8888 439.March 4-11 IWEPNM 95: International Winterschool on Electronic Properties of Novel Materials, Fullerides and Fulleroides Kirchberg, Tyrol, Austria Professor H. Kuzmany, Inst. f. Festkorperphysik der Universitat Wien, Strudlhofg. 4, A-1090 VieAna, Austria. March 5-10 ECLC 96: European Conference on Liquid Crystals Bovec, Slovenia Dr. Igor MuSeviE, ECLC 95, J. Stefan Institute, Jamova 39, P.O.B. 100, 61111 Ljubljana, Slovenia. E-mail: igor.musevic@ijs.si; Fax: +386 61 219385/273677. March 12-15 Second European East West Workshop on Chemistry and Energy Sintra, Portugal CBsar Sequeira, Instituto Superior Tecnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal. TeVFax: +351 1778 3594. March 13-15 Low-and No-VOC Coating Technologies: 2nd Biennial International Conference Durham, NC, USA Ms.Coleen M. Northeim, Research Triangle Institute, P.O. Box 12194,Research Triangle Park, NC 27709-2194, USA. Tel: +1 919 541 5816; Fax: +1 919 541 7155. March 19-22 FAMCC 1996: Florida Advanced Materials Chemistry Conference Palm Coast, FL, USA Daniel R. Talham, Department of Chemistry, University of Florida, Gainesville, FL 3261 1-7200, USA. Tel: +1 904 392 9016; Fax: +1 904 392 3255. March 29-31 British Liquid Crystal Society, Annual Conference Exeter, UK Professor Roy Sambles, Department of Physics, University of Exeter, Exeter, UK, EX4 4QL. April 2-6 Seventh Biennial Workshop on Organometallic Vapor Phase Epitaxy Fort Meyers, FL, USA TMS Meeting Services Department, 420 Commonwealth Drive, Warrendale, PA 15086, USA.E-mail: wilson@tms.org; Tel: +1 412 776 9000 ext. 241; Fax: +1 412 776 3770. April 3-6 ECIO '96: 7th European Conference on Integrated Optics Delft, The Netherlands ECI0'95 Secretariat, P.O. Box 5031, 2600 GA Delft, The Netherlands. Tel: +31 15 78 1034; Fax: +31 15 78 4046. April 24-26 19th International Power Sources Symposium 1995 Brighton, Sussex, UK T. Keily (Chairman), International Power Sources Symposium Committee, 1Oakley Drive, Fleet, Hampshire, UK, GU13 9PP. April 24-28 ICMCTF' 1995: International Conference on Metallurgical Coatings and Thin Films San Diego, CA, USA Mary S. Gray, ICMCTF 95, Suite 502,1090 G Smallwood Drive, Waldorf, MD 20603, USA. Tel: +1 301 870 8756; Fax: +1 301 645 1426.May 7-10 13th International Conference of Fluidized Bed Combustion Kissimmee, FL, USA Leslie Friedman, Meetings Manager, The American Society of Mechanical Engineers, 345 East 47&Street, New York, NY 10017-2392,USA. Tel: +1212 705 7788; Fax: +1 212 705 7856. May 9-13 7th International Conference on Indium Phosphide and Related Materials Sapporo, Hokkaido, Japan IEEELEOS, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA. Tel: +1 908 562 3893; Fax: +1 908 562 8434. 11 May 21-26 May 28-June 2 May 29-June 2 June 6-9 June 21-23 June 26-30 July 17-20 July 24-27 August 7-1 1 August 19-25 August 27-September 1 0 September 6-7 September 11-14 September 11-15 September 11-16 September 13-15 September 17-2 1 CLEO/QELS: Conference on Lasers and Electro-optics & Quantum Electronics and Laser Science Conference Baltimore, MD, USA IEEEYLEOS, 445 Hoes Lane, P.O.Box 1331, Piscataway, NJ 08855-1331, USA. Tel: +1908 562 3893; Fax: +1 908 562 8434. 2nd Mediterranean Workshop and Technical Meeting-Novel Optical Materials and Applications Cetraro, Italy Prof. I.C. Khoo, Electrical Engineering Department, Pennsylvania State University, University Park, PA 16802, USA. Tel: +1814 863 2299; Fax: +1814 865 7065. COLA '95: The Third International Conference on Laser Ablation Strasbourg, France E. Fogarassy, CNRS, Laboratoire Phase, BP 20, 67037 Strasbourg Cedex 2, France. Tel: +33 88 10 62 57; Fax: +33 88 10 62 93. 4th International Symposium on Metallomesogens Cetraro, Italy Dr. Francesco Neve, Dipartimento di Chimica, Universita della Calabria, 87030 Arcavacata di Rende, (CS), Italy.Fax: +39 984 492044. International Liquid Crystal Workshop on Surface Phenomena St. Petersburg, Russia Research Centre, Vavilov State Optical Institute, Birzhevaya Line 12, 199034, St. Petersburg, Russia. Fax: +7 812 218 13 35. 10th International Conference on Integrated Optics and Optical Fiber Communication Hong Kong BDG Communications Mgmt Ltd., IOOC'95 Conference Secretariat, Suite 1104-5, East Town Building, 41 Lockhart Road, Hong Kong. Tel: +852 528 6136; Fax: +852 865 1528. MC': 2nd International Conference on Materials Chemistry Canterbury, Kent, UK Dr. J. D. Wright, Chemical Laboratory, University of Kent, Canterbury, Kent, UK, CT2 7NH.FLC '95: 5th International Conference on Ferroelectric Liquid Crystals Cambridge, UK Prof. W.A. Crossland, Northern Telecom Research Professor of Photophysics, Department of Engineering, University of Cambridge, Cambridge, UK. Fax: +44 1223 330662. EP2DS XI: Eleventh International Conference on the Electronic Properties of Two-Dimensional Systems Nottingham, UK Prof. L. Eaves (EP2DS XI Chairman), Department of Physics, University of Nottingham, Nottingham, UK, NG7 2RD. E-mail: ppzpcm@ppnl.nott.ac.uk; Fax: +44 115 9 515180. Clays and Clay Materials Science: Euroclay '95 Leuven, Belgium Professor P. Grobet, Secretary Euroclay '95, Centrum voor Oppervlaktechemie en Katalyse, K U Leuven, K Mercierlaan 92, B-5001 Heverlee, Belgium.Tel: +32 16 220931; Fax +32 16 295126. ISCOM'95: International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets Mittelberg, Kleinwalsertal, Austria ISCOM'95, Prof. Heimo J.Keller, Anorganisch Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany. Tel: +49 6221 562 438; Fax: +49 6221 564 197. ICAC 95: Fourth International Conference on Automated Composites Nottingham, UK Conference Department (C527), The Institute of Materials, 1Carlton House Terrace, London, UK, SWlY 5DB. Tel: +44 171 235 1391; Fax: +44 171 823 1638. Euro-Fillers 95: International Conference on Fillers in Polymers Mulhouse, France Dr. E. Papirer, CRPCSS-CNRS, 24 av.Pdt. Kennedy, F-68200 Mulhouse, France. Tel: +33 89 42 01 55; Fax: +33 89 32 09 96. Electrochem '95 Bangor, Wales Dr. Maher Kalaji, Department of Chemistry, University of Wales, Bangor, Gwynedd, Wales, UK, LL57 2UW. Tel: +44 1248 351151 ext. 2516; Fax: +44 1248 370528. LB7:The Seventh International Conference on Organized Molecular Films Numana, Ancona, Italy Dr. M. G. Ponzi Bossi, Scientific Secretary LB7,Istituto di Scienze Fisiche, Facolta' di Medicina e Chirurgia, via Ranieri 65, 60131 Ancona, Italy. E-mail: fismed@anfisi.cineca.it;Tel: +39 71 220 4606; Fax: +39 71 220 4605. EuroOMet '95 incorporating the 29th Metallographie-Tagung Friedrichshafen, Germany Deutsche GesellschaR fur Materiakunde e.v., Adenauerallee 21, D-61440 Oberursel, Germany.Tel:+49 6171 4081; Fax:+49 6171 52554. 2-ICPEPA 2nd International Conference on Photo-Excited Processes and Their Applications Jerusalem, Israel Organizing Committee: ICPEPA-2, Professor A. Peled, Chairman, CTEH aff. Tau, 52 Golomb St., Holon 58102, Israel. E-mail: photoexe@ilctehol.bitnet;Tel: +972 3 502 8902; Fax: +972 3 502 8967. ... 111 September 25-29 Workshop on Non-Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials Pisa, Italy Dr. Dino Leporini, Dipartimento di Fisica, Universita di Pisa, Piazza Torricelli, 2 1-56100 Pisa, Italy. E-mail: leporini@ipifidpt.difi.unipi.it;Tel: +39 50 911284; Fax: +39 50 48277. September 25-29 OLC '95: VIth International Topical Meeting on Optics of Liquid Crystals Jk Touquet, France Prof.M. Warenghem, OLC '95, C.R.U.A.L., Faculte Jean Perrin, Rue J.Souvraz,S.P. 18, F 62307 Lena Cedex, France. E-mail: warenghem@lip5nx.decnet.citilille.fr; Tel: +33 20 43 48 12; Fax: +33 20 43 40 84. October 9-12 27th International SAMPE Technical Conference Albuquerque, NM, USA Dr. Charles L. Hamermesh, SAMPE Technical Director, 1161 Parkview Drive, Covina, CA 91724 USA. Tel: +1 818 331 0616 ext. 602; Fax: +1 818 332 8929. October 16-18 Asia Display '95 Hamamatsu, Japan Asia Display '95 Secretariat, do The Convention, Annecy Aoyama, 2F 2-6-12, Minami-Aoyama, Minato-ku, Tokyo 107, Japan. October 18-20 MOC '95: 5th Microoptics Conference Hiroshima, Japan K. Iga, Representative of the Microoptics Group, Optical Society of Japan (JSAF'),Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama, Japan 227.Tel: +8145 922 1111ext.2064; Fax: +8145 921 0898. 0 October 30- 3rd Brazilian Polymer Conference November 2 Rio de Janeiro, Brazil Professor Ailton Gomes. Fax: +5521 270 1317 or +5516 272 2892 December 3-8 loth International Conference on Solid State Ionics Singapore B. V. R. Chowdari, Department of Physics, National University of Singapore, Singapore-0511. E-mail: phychowd@leonis.nus.sg; Tel: +65 772 2956; Fax: +65 777 6126. 1996 June 24-28 ILCC: 16th International Liquid Crystal Conference Kent, OH, USA 16th International Liquid Crystal Conference, Liquid Crystal Institute, Kent State University, P.O.Box 5190, Kent, OH 44242-0001, USA.E-mail: 1LCClWalice.kent.edu; Tel: +1216 672 2654; Fax: +1 216 672 2796. August 4-9 IUPAC MACRO SEOUL '96: 36th IUPAC International Symposium on Macromolecules Seoul, Korea Dr. Kwang Ung Kim, Secretariat of IUPAC MACRO SEOUL '96, Division of Polymers, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Korea. E-mail: iupa&kistmail.kist.re.kr; Tel: +822957 6104; Fax:+82 2 957 6105. 0 Denotes a new or amended entry this month Entries in the Conference Diary are published free of charge. If you wish to include an announcement please send full details to: Journal of Materials Chemistry Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK, CB4 4WF Tel: +44 1223 420066; Fax: +44 1223 426017 iv Journal of Materials Chemistry Information for Authors Journal of Materials Chemistry is a monthly journal for the publication of original research papers (articles), feature articles and communications focusing on the chemistry of novel materials.There is no page charge for papers published in Journal of Materials Chemistry. Scope of the Journal Chemistry of materials, particularly those associated with areas of advanced technology: the modelling of materials, their synthesis and structural characterisation, physicochemical aspects of their fabrication, properties and applications. Materials Znorganics: ceramics; layered materials; microporous solids and zeolites; silicates and synthetic minerals; biogenic minerals.Organics: organometallic precursors for thin filmdceramics; novel molecular solids and synthetic polymers with materials applications; polymer composites; biopolymers; biocompatible and biodegradable polymers; liquid crystals (both lyotropic and thermotropic); Langmuir- Blodgett films. Properties and Applications Electrical properties: semi-, metallic and super-conductivity; ionic conductivity; mixed ionidelectronic conductivity; ferro-, pyro- and piezo-electricity; electroceramics; dielectrics. Optical properties: luminescence, phosphorescence, laser action; non- linear optical effects; photoconductivity; photo- and electro-chromism, resists, glasses, amorphous semiconductors; optical modulation and switching. Magnetic properties: ferro-, ferri- and antiferro-magnetism, spin glass behaviour, organic magnetism, magnetic bubbles and information storage.Chemical properties: ion exchange, molecular separation, catalytic action, sensor action, topochemical control of reactions. Structural properties: structural ceramics, refractories; hard materials; protective coatings; composites, adhesives, prosthetic applications. Thermodynamic properties and phase behaviour Articles Full papers contain original scientific work that has not been published previously. However, work that has appeared in print in a short form such as a Materials Chemistry Communication or Chemical Communication is normally acceptable. But note that the Society strongly discourages the fragmentation of a substantial body of work into a number of short publications.Papers should be typewritten in double spacing on one side only of the paper. Four copies of text, illustrations (full colour copies for coloured figuredplates), tables and any other matter should be sent to: The Editor, Journal of Materials Chemistry, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK All authors submitting work for publication are required to sign an exclusive copyright license. All submissions should be accompanied by a completed form (a blank one for photocopying is reproduced at the end of these instructions), without which publication cannot proceed. Feature Articles Feature Articles are published by invitation of the Materials Chemistry Editorial Board.Materials Chemistry Communications Materials Chemistry Communications contain novel scientific work in short form and of such importance that rapid publication is desirable. Authors should briefly indicate in a covering letter the reasons why they feel that publication of their work as a Communication is justified. The total length is normally restricted to two printed A4 pages. However, special consideration will be given to papers containing a large amount of essential diagrammatic material. Submission of a Materials Chemistry Communication 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 via a member of the International Advisory Editorial Board.In the latter case, the top copy of the manuscript including any figures etc., together with the name of the person to whom the Communication is being submitted, should be sent simultaneously to The Editor at the Cambridge address. Authors may wish to contact the Board member to ensure that he is available to arrange review of the manuscript within reasonable time. Administration Receipt of a paper will be acknowledged, and the paper will be given a reference number which authors are asked to quote on all their subsequent correspondence. If no such acknowledgement has been received after a reasonable period of time authors should check with the Editorial Office as to whether the paper or the acknowledgement has gone astray.Editorial Policy. Every paper (except Communications) will be submitted to at least two referees, by whose advice the Materials Editorial Board will be guided as to its acceptability. Full details are given in Refereeing Procedure and Policy, J. Muter. Chem., 1995, Issue 1. Papers that are accepted must not be published elsewhere except by permission of the Royal Society of Chemistry. Submission of a manuscript will be regarded as an undertaking that the same material is not being considered for publication by another journal. Conditions governing acceptance are available from the Editorial Office. Copyright. The whole of the literary matter (including tables, figures, diagrams and photographs) in Journal of Materials Chemistry is subject to copyright and may not be reproduced without permission from The Royal Society of Chemistry and such other owner of the copyright as may be indicated.Reprints. Fifty reprints of each paper are supplied free of charge on request. Notes on the Preparation of Papers 1. Manuscripts must by typed in double-line spacing, single sided on A4 paper, with margins at top, bottom and left-hand side of at least 4 cm. 2. The first page should be set out as follows: (i) Name and address of the author to whom the proofs and correspondence should be sent. (ii) Title of the paper, with capitals for the first letter of each noun and adjective only. (iii) Authors’ names, including one forename for each author.(iv) The address where the work was carried out; if this is different from the current address of any author wishing to deal with correspondence a footnote indicating the present address of this author should be included. (v) Abstract, preceded and followed by a horizontal line, and typed in double-line spacing. V GraphicalAbstracts 3. Suitable headings and sub-headings should be used in the main text as appropriate (except for Communications in which no headings are used). 4. References should be numbered serially in the text by means of superscript arabic numerals. 5. Bibliographic references (not footnotes) should follow the main text and should have the following format: 1 R.M.Barrer and R.J.B. Craven, J. Chem. SOC., Faraday Trans. 1, 1987,83, 779. 2 R.M. Barrer and R.J.B. Craven, in New Developments in Zeolite Science and Technology, ed. Y. Murakame, A. Iijima and J.W. Ward, Kodansha, Tokyo, 1986, p.521. 6. Journal titles should be abbreviated according to the Chemical Abstracts Service Source Index (CASSI). 7. Tables should be typed on separate sheets at the end of the manuscript. 8. Diagrams should be accompanied by a separately typed set of captions. Extensive identifying lettering should be placed in the captions rather than on the figures. Original artwork should be supplied wherever possible. Colour photographs will be accepted subject to approval by the referees.9. Bulk information (such as primary kinetic data, computer programs and output, etc) which accompanies papers published in Journal of Materials Chemistry may be deposited, free of charge, with the Society’s Supplementary Publications Scheme, either at the request of the author and with the approval of the referees or on the recommendation of the referees with the approval of the author. Details are available from the Editorial Office. Crystallographic Papers Crystallographic work will be assessed mainly for its relevance to materials. Papers reporting only the results of crystal structure determination may be accepted for publication provided they are for materials with potentially interesting properties. Crystallographic work that forms parts of a wider study, including synthesis or property measurements, should not normally be submitted for publication separately from the results of that study.Papers containing new crystal data should normally make explicit mention of this in the title. The description of a crystallographic structure determination should be as brief as possible; in particular, it is not the policy of the journal to publish lengthy data tables. For publication as part of their papers authors should include: a table of final fractional atomic coordinates (but without anisotropic temperature factors); a table of key bond lengths and angles; and a conventional line drawing of the structure. Additional data (any calcuIated coordinates; full list of bond lengths and angles; thermal parameters; structure factors; least-square planes) should be submitted as supplementary material for use by the referees.Apart from the structure factors this material will be deposited at the Cambridge Crystallographic Data Centre, 12Union Road, Cambridge CB2 1EZ (for molecules with organic carbon) or the Fachinformationszentrum Karlsruhe, D-7514 Eggenstein-Leopoldshafen 2 (otherwise). Any request to Cambridge or the Fachinformationszentrum Karlsruhe for deposited material should be accompanied by the full literature citation for the paper concerned. Full details regarding presentation of crystallographic work can be obtained from the Editorial Office. A graphical abstract should accompany each submission (a template for photocopying appears in issue 1).Authors are strongly encouraged to use diagrams or formulae only; the use of text will be allowed only when there is no alternative. Nomenclature Current IUPAC nomenclature and symbolism should be used. Attention is drawn to the following publications in which the rules themselves and guidance on their use are given: Nomenclature of Inorganic Chemistry, Blackwell Scientific Publications, Oxford, 1990. Nomenclature of Organic Chemistry, Blackwell Scientific Publications, 1993 edn. Biochemical Nomenclature and Related Documents, The Biochemical Society, London, 1978. Compendium of Chemical Technology: IUPAC Recommendations, Blackwell Scientific Publications, Oxford, 1987. Units and Symbols The recommendations of IUPAC should be followed. Their basis is the Systeme Internationale d’Unit6s 61).A detailed treatment is given in the so-called Green Book Quantities, Units and Symbols in Physical Chemistry, Blackwell Scientific Publications, Oxford, 1993 edn. PowderData Powder X-ray diffraction data may be published, preferably in tabular form, but should be restricted to studies of new materials; also, for cases where the materials are new but have similar powder data to other, well characterized, materials, such data will not usually be included in the journal. However, for the purposes of refereeing, a full data set in tabular form should be submitted as supplementary material, simultaneously with the paper; this material will subsequently be deposited with the Society’s Supplementary Publications Scheme (details available from the Editorial Office). Diagrams showing diffraction patterns of reaction products will not normally be included in the journal, unless they have some distinct feature of particular relevance to the discussion.vi INSTRUCTIONS FOR AUTHORS (1 995) APPENDIX IUPAC Publications on Nomenclature and Symbolism 1.O Compilations I. 1 Nomenclature of Organic Chemistry, a 550-page hardcover volume published in 1979, available from Pergamon, Oxford. Section A: Hydrocarbons Section B: Fundamental heterocyclic systems Section C: Characteristic groups containing carbon, hy- drogen, oxygen, nitrogen, halogen, sulfur, selenium and tellurium Section D:Organic compounds containing elements not exclusively those referred to in the title of Section C Section E: Stereochemistry Section F: General principles for the naming of natural products and related compounds Section H: Isotopically modified compounds 1.2 A Guide to IUPAC Nomenclature of Organic Compounds, a 182-page hardcover volume published in 1993, available from Blackwell Scientific Publications, Oxford, to be used in conjunction with item 1.1.1.3 Nomenclature of Inorganic Chemistry, a 278-page hardcover volume published in 1990, available from Blackwell Scientific Publications, Oxford. Chapter 1: General aims, functions and methods Chapter 2: Grammar Chapter 3: Elements, atoms and groups Chapter 4: Formulae Chapter 5: Names based on stoichiometry Chapter 6: Neutral molecular compounds Chapter 7: Names for ions, substituent groups and radicals, and salts Chapter 8: Oxoacids and derived anions Chapter 9: Co-ordination compounds Chapter 10: Boron hydrides and related compounds I .4 Biochemical Nomenclature and Related Documents, a 348-page softcover manual published in 1992 by Portland Press Ltd.for IUBMB, and available from the publisher (59 Portland Place, London WIN 3AJ, UK). The contents are as follows: Nomenclature of organic chemistry. Section E: Stereo-chemistry (I 974) Nomenclature of organic chemistry. Section F: Natural products and related compounds (1976) Isotopically modified compounds Recommendations for the presentation of thermodynamic and related data in biology (1985) Citation of bibliographic references in biochemical journals (1971) Nomenclature and symbolism for amino acids and peptides (1983) Abbreviated nomenclature of synthetic polypeptides or polymerized amino acids (1 97 1) Abbreviations and symbols for the description of the conformation of polypeptide chains (1 969) Nomenclature of peptide hormones (1 974) Nomenclature of glycoproteins, glycopeptides and peptidoglycans (1985) Nomenclature of initiation, elongation and termination factors for translation in eukaryotes (1988) Nomenclature of multiple forms of enzymes (1976) Symbolism and terminology in enzyme kinetics (1 981) Nomenclature for multienzymes (1 989) Abbreviations and symbols for nucleic acids, poly-nucleotides and their constituents (1970) Abbreviations and symbols for the description of the conformations of polynucleotide chains (1982) Nomenclature for incompletely specified bases in nucleic acid sequences (I 984) Carbohydrate nomenclature.Part I (1 969) Nomenclature of cyclitols (1 973) Numbering of atoms in myo-inositol(1988) Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives (1980) Nomenclature of unsaturated monosaccharides (1 980) Nomenclature of branched-chain monosaccharides (1980) Abbreviated terminology of oligosaccharide chains (1980) Polysaccharide nomenclature (1980) Symbols for specifying the conformation of polysaccharide chains (1 981) Nomenclature of lipids (1976) Nomenclature of steroids (1989) Nomenclature of quinones with isoprenoid side chains (1973) Nomenclature of carotenoids (1 970) and amendments (1974) Nomenclature of tocopherols and related compounds (1981) Nomenclature of vitamin D (1981) Nomenclature of retinoids (1 981) Prenol nomenclature (1 986) Nomenclature of phosphorus-containing compounds of biochemical importance (I 976) Nomenclature and symbols for folic acids and related compounds (1 986) Nomenclature for vitamins B-6 and related compounds (I 973) Nomenclature of corrinoids (1973) Nomenclature of tetrapyrroles (1986) 1.5 Compendium of Analytical Nomenclature, a 280-page hardcover volume published in 1987, available from Blackwell Scientific Publications, Oxford.The contents are as follows: Presentation of the Results of Chemical Analysis Solution Thermodynamics (activity coefficients, equilibria, PH)Recommendations for Terminology to be used with Precision Balances Recommendations for Nomenclature of Thermal Analysis Recommendations for Nomenclature of Titrimetric Analysis Electrochemical Analysis Analytical Separation Processes (precipitation, liquid- liquid distribution, zone melting and fractional crystallis- ation, chromatography, ion exchange) Spectrochemical Analysis (radiation sources, general atomic emission spectroscopy, flame spectroscopy, X-ray emission spectroscopy, molecular methods) Recommendations for Nomenclature of Mass Spec-trometry Recommendations for Nomenclature of Radiochemical Methods Surface Analysis (including photoelectron spectroscopy) vii 1.6 Compendium of Macromolecular Nomenclature, a 172-page hardcover volume published in 199 1, available from Blackwell Scientific Publications, Oxford.The contents are as follows: Basic Definitions of Terms Relating to Polymers Stereochemical Definitions and Notations Relating to Polymers Definitions of Terms Relating to Individual Macromolecules, their Assemblies, and Dilute Polymer Solutions Definitions of Terms Relating to Crystalline Polymers Nomenclature of Regular Single-strand Organic Polymers Nomenclature for Regular Single-strand and Quasi-single- strand Inorganic and Coordination Polymers Source-based Nomenclature for Copolymers A Classification of Linear Single-strand Polymers Use of Abbreviations for Names of Polymeric Substances 1.7 Compendium of Chemical Terminology: IUPAC Recommendations, a 456-page volume published in 1987, available in hardcover and softcover from Blackwell Scientific Publications, Oxford.1.8 Quantities, Units and Symbols in Physical Chemistry, a 166-page softcover volume published in 1993 by Blackwell Scientific Publications, Oxford. 2.0 Documents not included in the compil- ations 2.1 Nomenclature of Elements and Compounds Boron Compounds Nomenclature of inorganic boron compounds (Pure Appl. Chem., 1972,30,681). Delta Convention Nomenclature for cyclic organic compounds with contiguous formal double bonds (Pure Appl.Chem;, 1988,60, 1395). Elements Recommendations for the names of elements of atomic number greater than 100 (Pure Appl. Chem., 1979,51,381). Enzymes Enzyme Nomenclature (1 992), published by Academic Press in hardcover and softcover editions. Heterocyclic Compounds Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles (Pure Appl. Chem., 1983, 55,409). Hydrogen Names for hydrogen atoms, ions and groups, and for reactions involving them (Pure Appl. Chem., 1988,60, 1115). Isotopically Mod$ed Compounds Nomenclature of inorganic chemistry. Part 11. 1. Isotopically modified compounds (Pure Appl. Chem., 1981,53, 1887). Lambda Convention Treatment of variable valence in organic nomenclature (Pure Appl. Chem., 1984,56,769).Nitrogen Hydrides Nomenclature of hydrides of nitrogen and derived cations, anions and ligands (Pure Appl. Chem., 1982,54,2545). Numerical Terms Extension of Rules A- 1.1 and A-2.5 concerning numerical terms used in organic chemical nomenclature (Pure Appl. Chem., 1986,58, 1693). Polyanions Nomenclature of polyanions (Pure Appl. Chem., 1987,59,1529). Polymers Nomenclature of regular double-strand (ladder and spiro) organic polymers (Pure Appl. Chem., 1993,65, 1561). Structure-based nomenclature for irregular single-strand organic polymers (Pure Appl. Chem., 1994,66,873). INSTRUCTIONS FOR AUTHORS (1995) Radicals and Ions Revised nomenclature for radicals, ions, radical ions and related species (Pure Appl.Chem., 1993,65, 1357). Zeolites Chemical nomenclature and formulation of compositions of syntheticand natural zeolites (Pure Appl. Chem., 1979,51,1091). 2.2 Terminology, Symbols and Units, and Presentation of Results General Glossary of terms used in physical organic chemistry (Pure Appl. Chem., 1994,66, 1077). Glossary of atmospheric chemistry terms (Pure Appl. Chem., 1990,62,2 167). English-derived abbreviations for experimental techniques in surface science and chemical spectroscopy (Pure Appl. Chem., 1991,63, 887). Analytical Recommendations for publication of papers on a new analytical method based on ion exchange or ion-exchange chromatography (Pure Appl. Chem., 1980,52,2555).Recommendations for presentation of data on compleximetric indicators, 1. General (Pure Appl. Chem., 1979,51, 1357). Recommendations for publishing manuscripts on ion-selective electrodes (Pure Appl. Chem., 1981,53, 1907). Recommendations on use of the term amplification reactions (Pure Appl. Chem., 1982,54,2553). Recommendations for the usage of selective, selectivity and related terms in analytical chemistry (Pure Appl. Chem., 1983, 55, 553). Nomenclature for automated and mechanised analysis (Pure Appl. Chem., 1989,61, 1657). Nomenclature for sampling in analytical chemistry (Pure Appl. Chem., 1990,62, 1193). Nomenclature for chromatography (Pure Appl. Chem., 1993, 65, 8 19). Nomenclature of kinetic methods of analysis (Pure Appl.Chem., 1993,65, 2291). Nomenclature for liquid-liquid distribution (solvent extraction) (Pure Appl. Chem., 1993,65,2373). Nomenclature for supercritical fluid chromatography and extraction (Pure Appl. Chem., 1993,65,2397). Nomenclature and terminology for analytical pyrolysis (Pure Appl. Chem., 1993,65,2405). Nomenclature for the presentation of results of chemical analysis (Pure Appl. Chem., 1994,66, 595). Recommendations for nomenclature in laboratory robotics and automation (Pure Appl. Chem., 1994,66,609). Biotechnology Glossary for chemists of terms used in biotechnology (Pure Appl. Chem., 1992,64,143). Selection of terms, symbols and units related to microbial processes (Pure Appl. Chem., 1992,64, 1047). Clinical Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Pure Appl.Chem., 1984,56, 567). Quantities and units in clinical chemistry (Pure Appl. Chem., 1979,51,2451). Quantities and units in clinical chemistry: nebulizer and flame properties in flame emission and absorption spectrometry (Pure Appl. Chem., 1986,58, 1737). List of quantities in clinical chemistry (Pure Appl. Chem., 1979, 51,2481). Proposals for the description and measurement of carry-over effects in clinical chemistry (Pure Appl. Chem., 1991,63, 301). Quantities and units for metabolic processes as a function of time (Pure Appl. Chem., 1992,64, 1569). ... Vlll INSTRUCTIONS FOR AUTHORS (1995) Quantities and units for electrophoresis in the clinical laboratory (Pure Appl.Chem., 1994,66,891). Quantities and units for centrifugation in the clinical laboratory (Pure Appl. Chem., 1994,66,897). Colloids and Surface Chemistry Definitions, terminology and symbols in colloid and surface chemistry. I (Pure Appl. Chem., 1972, 31, 577). 11, Hetero- geneous catalysis (Pure Appl. Chem., 1976, 46, 71). Part 1.14: Light scattering (provisional) (PureAppl. Chem., 1983,55,931). Reporting experimental pressure-area data with film balances (Pure Appl. Chem., 1985,57,621). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Pure Appl. Chem., 1985,57,603). Reporting data on adsorption from solution at the solid/ solution interface (Pure Appl.Chem., 1986,58, 967). Manual on catalyst characterization (Pure Appl. Chem., 1991, 63, 1227). Thin films including layers: terminology in relation to their preparation and characterization (Pure Appl. Chem., 1994, 66, 1667). Electrochemistry Nomenclature for transfer phenomena in electrolytic systems (Pure Appl. Chem., 1981,53, 1827). Electrode reaction orders, transfer coefficients and rate constants-amplification of definitions and recommendations for publication of parameters (PureAppl. Chem., 1980,52,233). Classification and nomenclature of electroanalytical techniques (Pure Appl. Chem., 1976,45,81). Recommendations for sign conventions and plotting of electrochemical data (Pure Appl.Chem., 1976,45, 131). Electrochemical nomenclature (PureAppl. Chem., 1974,37,499). Recommendations on reporting electrode potentials in non- aqueous solvents (Pure Appl. Chem., 1984,56,461). Definition of pH scales, standard reference values, measurement of pH and related terminology (PureAppl. Chem., 1985,57,531). Interphases in systems of conducting phases (Pure Appl. Chem., 1986,58,437). The absolute electrode potential: an explanatory note (Pure Appl. Chem., 1986,58,955). Electrochemical corrosion nomenclature (Pure Appl. Chem., 1989,61, 19). Terminology in semiconductor electrochemistry and photo- electrochemical energy conversion (Pure Appl. Chem., 1991,63, 569). Nomenclature, symbols, definitions and measurements for electrified interfaces in aqueous dispersions of solids (PureAppl.Chem., 1991,63,895). Nomenclature, symbols and definitions in electrochemical engineering (Pure Appl. Chem., 1993,65, 1009). Terminology and conventions for microelectronic ion-selective field effect transistor devices in electrochemistry (Pure Appl. Chem., 1994,66,565). Kinetics Symbolism and terminology in chemical kinetics (provisional) (Pure Appl. Chem., 1981,53,753). Kinetics of composite reactions in closed and open flow systems (Pure Appl. Chem., 1993,65,2641). Photochemistry Recommended standards for reporting photochemical data (Pure Appl. Chem., 1984,56,939). Glossary of terms used in photochemistry (Pure Appl. Chem., 1988,60, 1055). Quantum Chemistry Expression of results in quantum chemistry (Pure Appl.Chem., 1978,50, 75). Reactions Nomenclature for organic chemical transformations (Pure Appl. Chem., 1989,61, 725). System for symbolic representation of reaction mechanisms (Pure Appl. Chem., 1989,61,23). Detailed linear representation of reaction mechanisms (Pure Appl. Chem., 1989,61, 57). Rheological Properties Selected definitions, terminology and symbols for rheological properties (Pure Appl. Chem., 1979,51, 1215). Spectroscopy Recommendations for publication of papers on methods of molecular absorption spectrophotometry in solution (Pure Appl. Chem., 1978,50, 237). Recommendations for the presentation of infrared absorption spectra in data collections.A, Condensed phases (Pure Appl. Chem., 1978,50,231). Definition and symbolism of molecular force constants (Pure Appl. Chem., 1978,50, 1709). Nomenclature and conventions for reporting Mossbauer spectroscopic data (Pure Appl. Chem., 1976,45,211). Recommendations for the presentation of NMR data for publication in chemical journals. A, Proton spectra (Pure Appl. Chem., 1972,29,625). B, Spectra from nuclei other than protons (Pure Appl. Chem., 1976,45,217). Presentation of Raman spectra in data collections (Pure Appl. Chem., 1981,53, 1879). Names, symbols, definitions and units of quantities in optical spectroscopy (Pure Appl. Chem., 1985,57, 105). A descriptive classification of the electron spectroscopies (Pure Appl, Chem., 1987,59, 1343).Presentation of molecular parameter values for IR and Raman intensity (Pure Appl. Chem., 1988,60, 1385). Recommendations for EPR/ESR nomenclature and conven- tions for presenting experimental data in publications (Pure Appl. Chem., 1989,61,2195). Nomenclature, symbols, units and their usage in spectro-chemical analysis. VII. Molecular absorption spectroscopy, UV and visible (Pure Appl. Chem., 1988, 60, 1449); VITI. Nomenclature system for X-ray spectroscopy (Pure Appl. Chem., 1991,63,735); X. Preparation of materials for analytical atomic spectroscopy (Pure Appl. Chem., 1988, 60,1461); XII. Terms related to electrothermal atomization (PureAppl. Chem., 1992, 64, 253); XIII. Terms related to chemical vapour generation (PureAppl. Chem., 1992,64,261).Recommendations for nomenclature and symbolism for mass spectroscopy (Pure Appl. Chem., 1991,63, 1541). Symbols for fine and hyperfine structure parameters (Pure Appl. Chem., 1994,66, 571). Solid State Definitions of terms relating to phase transitions of the solid state (Pure Appl. Chem., 1994,66, 577). Thermodynamics A guide to procedures for the publication of thermodynamic data (Pure Appl. Chem., 1972,39, 395). Assignment and presentation of uncertainties of the numerical results of thermodynamic measurements (Pure Appl. Chem., 1981,53, 1805). Notation for states and processes; significance of the word ‘standard’ in chemical thermodynamics and remarks on commonly tabulated forms of thermodynamic functions (Pure Appl.Chem., 1982,54, 1239). Standard quantities in thermodynamics: fugacities, activities and equilibrium constants for pure and mixed phases (Pure Appl. Chem., 1994,66,533). Recommendations for nomenclature and tables in biochemical thermodynamics (Pure Appl. Chem., 1994,66,1641). Toxicology Glossary for chemists of terms used in toxicology (Pure Appl. Chern., 1993,65, 2003). ix JOURNALS OF THE ROYAL SOCIETY OF CHEMISTRY Refereeing Procedure and Policy (1995) 1.0 Contributions to Dalton, Perkin and Faraday Transactions, J. Mater. Chem., The Analyst, J. Anal. At. Spectrom. and J. Chem. Research 1.1 Introduction This document summarises the procedure used for assessing papers submitted to the four Transactions,J. Mater.Chem., The Analyst, J. Anal. At. Spectrom., and J. Chem. Research, and provides guidelines for referees engaged in this assessment. 1.2 Subject Matter Papers are submitted to the various journals according to subject matter. If it is felt that a paper would be published more appropriately in an RSC journal other than the one suggested by the author, the referee should inform the Editor. The topics covered by the various journals are as follows. Dalton Transactions (Inorganic Chemistry). All aspects of the chemistry of inorganic and organometallic compounds, including bioinorganic chemistry and solid-state inorganic chemistry; the applications of physicochemical techniques to the study of their structures, properties and reactions, including kinetics and mechanism; new or improved experimental techniques and syntheses.Faraday Transactions (Physical Chemistry and Chemical Physics). Gas-phase kinetics and dynamics; molecular beam kinetics and spectroscopy, photochemistry and photophysics; energy transfer and relaxation processes: laser-induced chemistry; spectroscopies of molecules, molecular and gas- phase complexes: quantum chemistry and molecular structure, statistical mechanics of gaseous molecules and complexes; spectroscopies, statistical mechanics and quantum theory of the condensed phase, computational chemistry and molecular dynamics; colloid and interface science, surface science, physisorption and chromatographic science, chemisorption and heterogeneous catalysis, zeolites and ion-exchange phenomena; electrode processes, liquids and solutions; solid-state chemistry (microstructures and dynamics); reactions in condensed phases; physical chemistry of macromolecules and polymers; materials science; thermodynamics; biophysical chemistry and radiation chemistry. Perkin Transactions I (Organic Chemistry).All aspects of organic and bio-organic chemistry. These include synthetic organic chemistry of all types, organometallic chemistry, chemistry and biosynthesis of natural products, the relationship between molecular structure and biological activity, the chemistry of polymers and biological macromolecules, and medicinal and agricultural chemistry where there is originality in the science. Perkin Transactions 2 (Physical Organic Chemistry).Physicochemical aspects of organic, organometallic, and bio- organic chemistry, including kinetic, mechanistic, structural, spectroscopic and theoretical studies. Such topics include structure-activity relationships and physical aspects of biological processes and of the study of polymers and biological macromolecules. Journal of Materials Chemistry. The chemistry of materials, particularly those associated with advanced technology; modelling of materials; synthesis and structural characterisation; physicochemical aspects of fabrication; chemical, structural, electrical, magnetic and optical properties; applications. The Analyst (Analytical Science). Theory and practice of all aspects of analytical chemistry, fundamental and applied, including inorganic and organic chemical, physical and biological methods in applications areas such as environmental, clinical, geological, industrial, veterinary, food, etc.Journal of Analytical Atomic Spectrometry. The development of fundamental theory, practice and analytical application of atomic spectrometric techniques, including ICP MS and XRF. Journal of Chemical Research. All areas of chemistry. The format of this journal (one- or two-page printed synopsis in Part S, plus microform version of authors’ full text typescript in Part M) makes it particularly suitable for papers containing lengthy experimental sections or extensive data tabulations. 1.3 Procedure Each manuscript is considered independently by two referees.The referees’ reports constitute recommendations to the appropriate Editorial Board, which is empowered to take final action on manuscripts submitted. The Editor, acting for the Editorial Board, is responsible for all administrative and executive actions, and is empowered to accept or reject papers. It is the Editor’s duty to see that, as far as possible, agreement is reached between authors and referees; although the referees may need to be consulted again concerning an author’s reply to comments, further refereeing will be avoided as far as possible. 1.3.1 Adjudication of disagreements. If there is a notable discrepancy between the reports of the two referees, or if the difference between authors and referees cannot be resolved readily, a third referee may be appointed as adjudicator.In extreme cases, differences may be reported to the appropriate Editorial Board for resolution. When a paper is recommended for rejection by referees, the Editor will inform the authors and return the top copy of the manuscript. Authors have the right to appeal to the Editorial Board if they regard a decision to reject as unfair. The Editor may refer to the Editorial Boards any papers which have been recommended for acceptance by the referees, but about which the Editor is doubtful. 1.3.2 Anonymity. The anonymity of referees is strictly preserved, and reports should be couched in terms which do not disclose the identity of the writer. A referee should never communicate directly with an author, unless and until such action has been sanctioned by the Society, through the Editor.1.3.3 Confidentiality. A referee should treat a paper received for assessment as confidential material. Information acquired by a referee from such a paper is not available for citation until the paper is published. X REFEREEING PROCEDURE AND POLICY (1995) 1.4 Policy The primary criterion for acceptance of a contribution for publication is that it should advance scientific knowledge significantly. Papers that do not contain new experimental results may be considered for publication only if they either reinterpret or summarise known facts or results in a manner presenting an advance in chemical knowledge.Papers in interdisciplinary areas are acceptable if the chemical content is considered satisfactory. Papers reporting results regarded as routine or trivial are not acceptable in the absence of other, desirable attributes. Although short papers are acceptable, the Society strongly discourages the fragmentation of a substantial body of work into a number of short publications; such fragmentation is likely to be grounds for rejection. The length of an article should be commensurate with its scientific content; however, authors are allowed every latitude (consistent with reasonable brevity) in the form in which their work is presented. Figures and flow-charts can often save space as well as clarify complicated arguments, and should not be excised unless they are unhelpful or really extrava- gant.The use of colour and/or half-tones is permitted in cases where genuine clarification results; referees are asked to advise on this. If a paper as a whole is judged suitable for the Journal, minor criticisms should not be unduly emphasised. It is the responsibility of the Editor to ensure the use of reasonably brief phraseology, and to assist the author to present his work in the most appropriate format. However, referees should not hesitate to recommend rejection of papers which appear incurably badly com-posed. It should be clearly understood that referees’ reports are made in confidence to the Editor, at whose discretion comments will be transmitted to the author.To assist the Editor, referees are requested to indicate which comments are designed only for consideration, as distinct from those which, in the referee’s view, require specific action or an adequate answer before the paper is accepted. Referees may ask for sight of supporting data not submitted for publication, or for sight of a previous paper which has been submitted but not yet published. Such requests must be made to the Editor, not directly to the author. 1.4.1 Authentication of new compounds. Referees are asked to assess, as a whole, the evidence in support of the homogeneity and structure of all new compounds. No hard and fast rules can be laid down to cover all types of compounds, but the Society’s policy is that evidence for the unequivocal identification of new compounds should wherever possible include good elemental analytical data; for example, an accurate mass measurement of a molecular ion does not provide evidence of purity of a compound and must be accompanied by independent evidence of homogeneity. Low-resolution mass spectrometry must be treated with even more reserve in the absence of firm evidence to distinguish between alternative molecular formulae.Where elemental analytical data are not available, appropriate evidence which is convincing to an expert in the field may be acceptable. Spectroscopic information necessary to the assignment of structure should normally be given. Just how complete this information should be must depend upon the circumstances; the structure of a compound obtained from an unusual reaction or isolated from a natural source needs much stronger supporting evidence than one derived by a standard reaction from a precursor of undisputed structure.Referees are reminded of the need to be exacting in their standards but at the same time flexible in their admission of evidence. It remains the Society’s policy to accept work only of high quality and to permit no lowering of standards. 1.5 Titles and Summaries Referees should comment on titles and summaries with the following points in mind. Titles of papers are used out of context by several organizations for current awareness purposes. To enable such systems to serve chemists adequately, titles must be written around a sufficient number of scientific words carefully chosen to cover the important aspects of the paper.Summaries should preferably be self-contained, so that they can be understood without reference to the main text. 1.6 Speed of Refereeing The Editorial Boards are anxious to maintain and to reduce further if possible the publication times now being achieved. In this connection, referees should submit their reports with the minimum of delay, or return manuscripts immediately to the Editor if long delay seems inevitable. 1.7 Suggestions of Alternative Referees The Editor welcomes suggestions of alternative referees competent to deal with particular subject areas. Such suggestions are particularly helpful in cases where referees consider themselves ill-equipped (in terms of specialist knowledge) to deal with a specific paper, and in highly specialized or new areas of research where only a limited number of experts may be available.If, in such a case, the alternative and the original referee work in the same institution, the manuscript may be passed on directly after informing the Editor. 1.8 Short Papers and Letters ‘Short Papers’ are published in J. Chem. Research. They are intended for the description of essentially complete pieces of work which can be described in two printed pages or less. They are NOT preliminary communications, nor in any way an alternative to Chemical Communications, for which there are additional criteria of novelty and urgency. The quality of material contained in a short paper should be the same as that in a full paper.Investigations arising out of some larger project but not prosecuted to the same degree are particularly appropriate for this format. A short paper should not normally exceed in length about 8 pages of typescript, including figures, tables, etc. It should comprise a one-sentence abstract and discussion, but adequate experimental details are required. As a consequence of its length, it appears in full in Part S with no microform version in Part M. ‘Letters’, published in Dalton Transactions, Analytical Proceedings, and The Analyst, are a medium for the expression of scientific opinions and views normally concerning material published in that journal; it is intended that contributions in this format should be published rapidly.The letters section is for scientific discussion, and is not intended to compete with media for the publication of more general matters such as Chemistry in Britain. Only rarely should a Letter exceed one printed column in length (about 1-2 pages of typescript). Where a letter is polemical in nature, and if it is accepted, a reply will be solicited from other parties implicated, for consideration for publication alongside the original letter. 1.9 Relationship with Communications Journals In cases where a preliminary report of the work described has appeared (for example in Chemical Communications), referees x1 REFEREEING PROCEDURE AND POLICY (1 995) should alert the editor to any excessive and unnecessary repetition of material; this can arise in connection with communications journals in which the restrictions on length and the reporting of experimental data are less severe than those of Chemical Communications.Furthermore, the acceptability of the full paper must be judged on the basis of the significance of the additional information provided, as well as on the criteria outlined in the foregoing sections. 2.0 Contributions to Chemical Communic-ations Chemical Communications is intended as a forum for preliminary accounts of original and significant work, in any area of chemistry that is likely to prove of wide general appeal or exceptional specialist interest. Such preliminary reports should be followed up in most cases by full papers in other journals, providing detailed accounts of the work.It is Society policy that only a fraction of research work warrants publication in Chemical Communications, and strict refereeing standards should be applied. The benefit to the reader from the rapid publication of a particular piece of work before it appears as- a full paper must -be balanced against the desirability of avoiding duplicate publication. The needs of the reader, not the author, must be considered, and priority in publication should not be allowed to determine acceptability. Acceptance should be recommended only if, in the opinion of the referee, the content of the paper is of such urgency or impact that rapid publication will be advantageous to the progress of chemical research.Communications should be brief and not exceed two pages in the printed form including Tables and illustrations -a maximum of 1500 words for a purely textual communication. Only in exceptional circumstances will a Communication be allowed to extend to four printed pages. Lengthy introductions and discussion, extensive data, -and excessive experimental details and conjecture should not be included. Figures and Tables will only be published if they are essential to understanding the paper. Referees may ask for sight of supporting data before reaching a decision. The refereeing procedure for Communications is the same as that for full papers, except that rapidity of reporting is crucial in order to maintain rapid publication.3.0 Communications submitted to Analytical Proceedings and J. Anal. At. Spectrom. Criteria for acceptance of communications submitted to Analytical Proceedings and J. Anal. At. Spectrom. are broadly similar to those for contributions to Chemical Communications, except that they should be concerned specifically with analytical chemistry. Scientific importance (rather than urgency) is the main criterion for acceptance. A decision whether or not to publish rests with the Editor, who will obtain advice from at least one referee. 4.0 Communications submitted to Perkin, Dalton or Faraday Transactions or J. Mater. Chem. Criteria for acceptance of Communications submitted to Perkin, Dalton or Faraday Transactions or J.Mater. Chem. are similar to those for contributions to Chemical Communications, except that the work will be of more specialist interest. For Perkin and Dalton Communications inclusion of key experi- xii mental data is expected. Assessment is carried out by a small nucleus of referees, consisting largely of members of the appropriate Editorial Boards. 5.0 Contributions to Mendeleev Communic- ations Mendeleev Communications, published jointly by the Royal Society of Chemistry and the Russian Academy of Sciences, is a sister publication to Chemical Communications, containing preliminary reports of the same type, in any area of chemistry. The majority of contributions are from Russian authors. Assessment involves two stages of refereeing.Manuscripts submitted to the Moscow Editorial Office are refereed initially by a Russian scientist. If found acceptable they are then reviewed by Western scientists chosen by the Royal Society of Chemistry. Manuscripts submitted to the UK Editorial Office undergo this two-stage refereeing process in reverse. 6.0 X-Ray Crystallographic Work 6.1 All papers containing crystallographic determinations will be refereed by two referees, one a structural chemist. If the editor considers it advisable, the paper may also be sent to a specialist crystallographer for comment. Referees will not normally be expected to check values of structural parameters for publication (e.g.bond lengths and angles against atomic co- ordinates; this will be done after publication by the appropriate crystallographic data centre), but should still pay attention to the quality of the experimental crystallographic work.However, their primary concern should be such new chemistry as is involved in the structure. 6.2 Papers will often contain the information in their titles that an X-ray structure determination has been carried out. However, this is not obligatory, especially if the X-ray determination forms only a minor part. Summaries should normally contain this information. 6.3 A structure referred to in a Communication will normally be fully refined. The Communication can then be considered to fulfil the archival function, and the structure determination may not require further detailed refereeing when presented as part of a full paper.In the full paper, the author’s purpose will then be served by a simple reference back to the original communication. However, if the crystallography is discussed again at any length in the full paper, the data should be re-presented to the referees in full, and re-published if considered necessary. 6.4 There may be other cases when an author wishes to publish a full paper in which the result of a crystal structure determination is discussed, but in which details or extensive discussion are considered unnecessary. The crystallographer may even be omitted as a co-author (for example when the determination is carried out by a commercial company). If the author is able to show the referees that this procedure is appropriate, it will be allowed provided that it does not lead to unnecessary fragmentation.However, the author must provide, as supplementary information, sufficient data relating to the crystal structure determination to allow a referee to make sure that the point made is correct, and co-ordinates etc. will be deposited. The brief published description of the determination should be supplemented by appropriate reference to ‘unpub- lished work’. Paper no (inserted by office): ROYAL SOCIETY OF CHEMISTRY EXCLUSIVE COPYRIGHT LICENCE Authors submitting manuscripts for publication in Royal Society of Chemist Journals are requested to read the notes below and to enclose with the manuscript a copy of this form, duly completed.Please type. or usc BLOCK ZAPITALS. 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ISSN:0959-9428    

DOI:10.1039/JM99505BP013

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995,5( l),27-30 Surface Properties and Biocompatibility of Ion-implanted Polymers Vaclav SvorEik," Vladimir Rybka," Vladimir Hnatowicz,b Lucie BaCakova," V&a Lisa" and FrantiSek Kocou re k" a Department of Solid State Engineering, Institute of Chemical Technology, 76628 Prague, Czech Republic Institute of Nuclear Physics, Czech Academy of Science, 250 68 Rel, Czech Republic " Institute of Physiology, Czech Academy of Sciences, 742 20 Prague, Czech Republic The surface properties of the polyethylene (PE), polypropylene (PP) and polystyrene (PS) samples doped with 150 keV F+ ions with doses of 1 x 101*-1 x 1015cm-2 have been characterized by different techniques and their biocompatibility to vascular smooth muscle cells was examined. The concentration and the conjugation length of the double bonds produced by ion impact, the conductivity and the surface polarity increased with the level of doping.The cell density was measured on the PP and PS samples doped with doses below 1 x 1013cm-2. The cells cultured on the ion-doped PS and PP exhibited better homogeneity and the resulting density was several times higher than that on the undoped polymers. No such effects were observed on the doped PE. The enhanced cell proliferation correlates with the increased surface polarity of the doped polymers. The biomedical properties such as wettability and blood compatibility of common polymers are far inferior to those of human body organs. Polymers are commonly employed in experimental medicine and clinical practice, e.g.for manufac- turing vessels for cell and tissue cultures, and for the pro- duction of artificial vascular grafts,' artificial joints2 and eye lenses3 It is very important to improve their surface properties in order to produce more effective clinical membrane^.^ Human cells are well known to have low adhesivity to unmodified polymers which exhibit hydrophobic properties.' Several procedures for enhancing the wettability and biocom- patibility of polymers have been described. Polytetrafluor- ethylene was treated in a low-temperature oxygen-nitrogen plasma in order to improve its surface properties.' Significant improvement of the biocompatibility of the same polymer was achieved by coating its surface with a 0.5 pm film of pyrolytic carbon6 or by hydroxylating the polymer surface via deposition of aluminium which was subsequently removed with sodium hydr~xide.~ Ion implantation is an efficient technique for semiconductor doping, for improving the wear and corrosion resistance of metals' and for modification of polymer surface^.^ Recently the effects of the ion implantation on polymer biocompatibility have been intensively studied and several encouraging results have been ~btained.~~~*'~ In this paper, the structure, surface polarity and electrical conductivity of PE, PP and PS doped with different amounts of 150 keV F+ ions were studied.The adhesion of vascular smooth muscle cells (VSMC) to the modified polymer surface was also studied in vitro in relation to the polymer surface characteristics.Experimental The present experiments were accomplished on 1.5 mm thick films of polymers with the common monomer unit -CH,-CHR,: PE (R=H, M= 1800O0, p=0.945 g ~m-~), PP (R=CH3, M=150000, p=0.901 g~m-~) and PS (RrC&, M=110000, p=1.05g~m-~). The polymer samples were doped at room temperature with 150 keV F+ ions with doses of 1x 10l2-1 x 1015 cm-2. The residual press- ure in the implanter target chamber was ca. lop4Pa. No additional treatment of the specimens was carried out before or after ion implantation and the doped samples were stored at room temperature in air in darkness. The UV-VIS spectra of the polymer samples were measured using a standard UV spectrophotometer and the results are presented as the difference between the absorbances of the doped and undoped polymers.The polar component of the surface Helmholtz energy, ysp, characterizing the polymer surface polarity, was determined by measuring the contact angle with a reflection goniometer." The surface structure of the polymer samples and the oxidation phenomena induced by ion implantation were studied by the standard RBS (Rutherford back-scattering) te~hnique.'~.'~ The sheet resis- tivity of the polymers at room temperature and under a pressure of ca. 1 Pa was measured by means of a Keithley device. The surface roughness of the doped polymers was determined by SEM. All doped specimens exhibited perfectly smooth surfaces with irregularities not exceeding the SEM resolution of ca.100 nm. The proliferation and adhesion of VSMC on the doped polymers was examined by the following procedure. The polymer samples 8 mm x 8 mm in size were sterilized in 96% ethanol and washed in deionized water. The samples were then glued with collagen onto the bottom of a Nunclon multidish ( 16 mm in diameter) and 20 000 smooth muscle cells derived from human aorta in 1.5 ml of Dulbecco's minimum essential medium supplemented with foetal calf serum ( 10%) and gentamycin (40 pg ml-') were added. The cell cultures were incubated at 37 "C and 90% humidity. After 18 or 96 h incubation the specimens were washed in phosphate-buffered saline, fixed in 3 :1 ethanol-acetic acid for 15 min and stained with toluidine blue.The population density of VSMC adhered to the polymers was evaluated after 18 h in vitro, when the cells were in lag phase and did not synthesize DNA and divide. The number of cells in 36 randomly chosen fields was determined visually with an optical microscope at an objective magnification of 100 x . The resulting cell density (cells ern-,) on the substrate was determined for two samples modified under the same conditions. Control experiments were per- formed on PS plates treated in a gas plasma (Gama Comp., Czech Republic), commonly used for cell cultivation and on a cover slip (Corning Comp., USA). Results and Discussion As was shown in our earlier papers, doping with Ff ions led to the production of carbonyl groups and conjugated double bonds on the polymer chains of PEI4 and PP.I5 The new groups and structural changes in general arose as a result of the rupture of chemical bonds by incoming ions followed by 28 free-radical recombination and subsequent oxidation of the polymer surface layer with ambient oxygen.The oxidation of the doped PE and PS was studied by RBS and the oxygen surface concentrations were studied as a function of the implanted ion dose (Table 1). For doses <5 x 1013 for PS or <1 x 1014 cm-2 for PE, no polymer oxidation was detected. For higher doses the oxygen concen- tration increased with the dose, but for the highest dose of 1 x 1015 cm-2 the oxygen concentration declined again. This decrease is probably due to significant carbonization of the polymer chain which, for very high doses, may lead to the creation of carbon clusters16 or to the production of long polyene sequences (vide infra).The polymer sensitivity to oxygen is known to be connected to the presence of tertiary hydrogens in the polymer m~lecule.’~The lower oxygen uptake (cf.PE) observed on PS doped with higher doses (see Table 1) can be explained by screening of tertiary hydrogens by the phenyl groups in the PS molecular chain. The concentration of the conjugated double bonds arising as a result of the ion implantation of polyolefins was deter- mined by UV-VIS spectrometry. The polymer absorbance in UV-VIS spectra is known to be closely related to the concen- tration and the length of conjugation of the double The measured absorbances as a function of the dose for the polymers under study are shown in Fig.1. The concentration and the conjugation length increase with the dose and signifi- cantly more conjugation is produced in PP than in PE. The much higher absorbance of PS samples is due to the presence of the aromatic ring in the PS macromolecule, which has three conjugated double bonds and exhibits a sharp absorp- tion edge at 290 nm. An increase in the electrical conductivity of polymers doped with doses of <1 x 1014cm-2 is often explained by the production of conjugated double bonds in the polymer chain.” For doses >1 x cm-2, however, the conductivity is affected also by the presence of carbon clusters.16 The measured dependence of the sheet resistivity, R,, on the dose Table 1 Oxygen concentration after Ff ion implantation (150 keV) into PE and PS oxygen concentration/lOzZ cmP3 dose/cm -‘ PE PS -0.65 1.11 1.03 1.99 1.07 1.11 0.70 wavelengt h/nm 200 250 300 400 600 800 1.2 0.8 0.4 0.0 50 40 30 20 10 wavenumbedl O3 cm-’ Fig.1 UV-VIS spectra measured for PE (-), PP (---) and PS (...) implanted with 150keV F+ ions at different doses. The numbers given represent the implanted doses. J. MATER. CHEM., 1995, VOL. 5 is shown in Fig. 2. For all the polymers studied, the sheet resistivity decreased slowly with increasing ion dose. For PS doped with the lowest dose of 1 x 10l2 cmP2 the resistivity lay well above the detection limit of ca.2 x 10l6 R. The conduc- tivity increase observed in this case is rather low in comparison with, e.g., that measured earlier on the polymers doped with Sb’ ions to the same degree.20 The difference is obviously related to the much lower concentration of defects produced by the lighter F+ ions and possibly by partial deterioration of the conjugated double bond system by its interaction with the reactive F+ ions.21 The polymer oxidation and the creation of oxidized struc- tures, e.g. carbonyl groups,14 on the polyolefin chains affects the polarity of the polymer surface. The measured dependence of the polar component of the surface Helmholtz energy ySp on the implanted ion dose is shown in Fig. 3. The non-zero polarity observed on the unimplanted polymers is probably due to the presence of additives, e.g.light stabilisers in the polymers. The polar component of ysp for all the polymers investigated increases with the implanted ion dose D IX 10” Fig. 2 Sheet resistivity (R,) as a function of the implanted dose for PE (O), PP (a)and PS (W). The experimental errors for Fig. 2-4 lie within the dimension of the symbols. 20 1 1 1 0 0 1x10~~ 1x10’~ 1x10~~ 1x10~~ dose/cm-2 Fig.3 Dependence of the polar component of ys* on the implanted ion dose for PE (O), PP (a)and PS (U) J. MATER. CHEM., 1995, VOL. 5 (ysP =log D),the smallest increase being observed for PE. The corresponding polar components of the reference Corning glass and Gama PS were y,P=49.5 and 14.6mJ m-2, respect- ively.Comparing Table 1 and Fig. 3 it can be seen that there is no direct, unambiguous relationship between the polymer surface polarity and the oxygen concentration. The surface polarity, at least for higher doses, has to be enhanced by another process that is perhaps connected with deterioration of the original polymer structure and related changes in the chemical state of oxygen or possibly with diffusion of additives towards the polymer surface and their accumulation on it, The latter effect, however, is not observed in the RBS spectra. The observed dependence of the VSMC density measured on PE, PP and PS samples after incubation times of 18 (chosen by chance) and 96 h is shown in Fig.4. The cell densities (d) measured on the doped samples should be compared with those obtained under the same conditions on reference samples of Gama PS and Corning glass: dPs= 11 930k630 ~m-~,d,,,,=3630+ 150 cm-' and dPs= 96450+4500 cm-2, dglass=185 340k4670 cm-2 for respective incubation times of 18 and 96 h. Because of the rather broad set of positions examined on the sample surface, the quoted errors in the cell density are supposed to characterize mostly the homogeneity of the cell proliferation which, for the reference samples, is <5%. Similar figures were obtained for increase in the VSMC density on PP. It may be concluded that, with some exceptions in limited dose ranges, there is no ""I 04!: unambiguous relationship between the measured surface I1111111 1 I1111111 I I I111111 I I llll111 0 1~1012 1x10'3 1x10'~ 1x10'~ polarity and the VSMC density.No direct relationship is found between the VSMC adhesion and proliferation and the dose/cm-* measured sheet resistivity or the oxygen uptake (cf. Table 1). all the doped samples, so it may be concluded that they exhibit the same homogeneity of cell proliferation as the reference samples. A slightly poorer homogeneity of cell proliferation (8-lOYo)was observed on the undoped polymers regardless of the incubation time. Fig. 4(a) shows that after 18 h incubation, a comparable cell density was observed for undoped PE and PP, but the density on undoped PS was significantly lower. The modifi- cation brought about by increasing the ion dose led to no significant change in the resulting cell density for the PE samples. For the PP samples a significant increase in the cell density was observed with increasing ion dose, so that the cell density on the PP implanted with the doses >1x cm-2 was ca.twice of that for PE modified under the same conditions. However, the most pronounced effect was observed on PS, for which the cell density increased rapidly with ion dose for doses <1 x lOI3 cm-2. Then, for higher doses, a significant decrease in the cell density was observed. An optimum ion dose of around 1 x lOI3 cm-2 exists for the cell adhesion where the cell density is by ca. one order of magni- tude higher than for undoped PS. Using this ion dose, the doped PS samples exhibited a cell density that is ca.50% higher than that on the reference Gama PS plates. The VSMC adhered on the PP and PS samples were found to be polygonal, indicating better spreading than on the PE samples, where most of cell population exhibited round shapes. A different picture was observed after 96 h incubation time [Fig. 4(b)]. While for the PE and PS samples, the cell density hardly altered with the dose, the observed cell density on the PP samples increased with the dose for doses <5 x 1OI2 cmP2. For higher doses a decrease in the cell density was observed, as in the case of PS. For a dose of 5 x 10" cm-2, the cell density was ca. three times higher than for undoped PP and ca. twice that of the reference Corning glass.These results confirm the factz2 that cell adhesion and proliferation depend strongly on the polymer type. In the case of the VSMC, ion implantation increases the biocompatibility of PS and PP significantly, while no effect is observed for PE. PS and PP exhibit better biocompatibility than the reference samples used in this study. The observed positive effects of ion implantation on VSMC proliferation and adhesion are in general agreement with the results obtained previously.1° The reasons for the increased cell adhesion and proliferation on doped polymers are still unclear. The improved biocom- patibility could be related to the presence of polar groups, e.g. hydroxy groups," produced by ion implantation, but other processes may play a significant role.Of the polymers investigated, PE exhibits for both incubation times the lowest VSMC density, independent of the implanted dose (Fig. 4). This correlates with the relatively slow increase in the PE surface polarity with implanted ion dose (Fig. 3). For PS and PP implanted with doses of <1x lOI3 cm-2, the surface polarity increases with the ion dose as does the VSMC density measured after 18 h incubation. For higher doses, however, the cell density declines and the correlation is lost. For implanted doses of >1x 1013 cm-2 and for the 18 h incu- bation, the measured VSMC densities on all polymers are roughly proportional to ysP. After 96 h incubation, however, the proportionality is destroyed due to an extraordinary Fig.4 Dependence of the density of the vascular smooth muscle cells For implanted doses >1 x 1014cmP2, the polymer structure PP (0)and PS (W) changed markedly and considerable carbonization took place (VSMC) on the implanted ion dose for PE (O), measured after (a) 18 h and (b)96 h incubation time due to escape of the more volatile products, and carbon 30 clusters may have been created. The resulting structure depended mainly on the energy density deposited by the implanted ions, regardless of the ionic species, but to a much smaller extent on the structure of the undoped polymer. The different cell densities measured on the different polymers implanted to the same high doses indicate the rather minor effects of the carbonization on the cell proliferation and adhesion.This contradicts a recent observation6 that cell proliferation may be enhanced by a deposited carbon layer. Conclusion The surface properties of PE, PP and PS implanted with 150 keV F+ ions at different doses were characterized. The ion implantation increases the electrical conductivity and the surface polarity of the polymers. The concentration and the conjugation length of the double bonds produced by the implantation increase with the implanted dose. Significant oxidation of the samples implanted to higher doses was observed. Biocompatibility, measured via proliferation and adhesion of VSMC, of doped PS and PP increases with the ion dose for doses -=1 x lOI3 cmP2.No clear correspondence between the measured VSMC density and the surface polarity, the oxygen uptake and the sheet resistivity was identified.The measured cell density depends in a rather complicated manner on the polymer structure, the implanted ion dose and the incubation time. Cell adhesion and proliferation on the doped polymers is more homogeneous than on the reference speci- mens. Additional experiments are underway to elucidate the mechanism of enhanced cell proliferation and adhesion on doped polymers. The authors thank Mr. I. Micek for help with the experiments. This work was partly supported by the Grant Agency of the Czech Republic under the contract no. 202/93/0121. References 1 H. Magometschnigg, M. Kadlec, M. Vodrazka, W. Dock, M. Grimm, M.Grabenwoger, E. Minar, M. Standacher, G. Fenzel and E. Wolner, J. Vasc. Surg., 1992,15,527. J. MATER. CHEM., 1995, VOL. 5 T. Rostbund, P. Thomsen, L. M. Bjursten and L. E. Ericson, J. Biomed. Mater. Res., 1990,24, 847. K. Smetana, J. Vacik, D. SouEkova and S. Pitrova, Clin. Muter., 1993,13,47. L. Dejun, Z. Iie, G. Hanging, L. Mozhu, D. Fuging and Z. Qiging, Nucl. Instr. Methods, 1993, B82, 57. A. Dekker, K. Reitsma, T. Bengeling, A. Bantjes, J. Feijen and W. G. van Aken, Biomaterials, 1991, 12, 130. R. Sbarbati, D. Giannessi, M. C. Cennim, G. Lazzerini, F. Verni and R. De Caterida, Znt. J.Artif. Organs 1991, 14,491. N. B. McKeown, G. Chang, 0. Niven, A. D. Romasch, G. J. Wilson, M. Thompson and P. G. Kalman, ASAZO Trans., 199 1,37, M477.8 M. Lwaki, CRC Crit. Rev. Solid State Muter. Sci., 1989, 15,473. 9 K. Kusakabe, H. Akiba and M. Lwaki, Nucl. Instr. Methods, 1991, B59/60,698. 10 Y. Suzuki, M. Kusakabe, J. S. Lee, M. Kaibara, M. Lwaki and H. Sasabe, Nucl. Znstr. Methods, 1992, B65, 142. 11 V. SvorEik, V. Rybka, K. Volka, V. Hnatowicz and J. Kvitek, Jpn. J. AppE. Phys., 1992, B31, 287. 12 J. F. Ziegler, J. P. Biersack and U. Littmark, in The Stopping and Ranges of Ions in Solids, Pergamon Press, New York, 1985. 13 J. P. Biersack and L. G. Haggmark, Nucl. Znstr. Methods, 1980, 174,257. 14 V. SvorEik, V. Rybka, R. EndrSt, V. Hnatowicz and J. Kvitek, J. Electrochem. SOC.,1993, 140, 549. 15 V. SvorCik, V. Rybka, K. Volka and J. Kvitek, Appl. Phys. Lett., 1992,61,1168. 16 M. Lwaki, K. Yabe, A. Fukuda, H. Watanabe, A. Ltoh and M. Takeda, Nucl. Instr. Methods, 1993, B80/81, 1080. 17 B. Doleiel, Die Bestandigkeit von Kunststofen und Gummi, Hanser, Munchen, 1978. 18 B. Ranby and J. F. Rabek, in Photodegradation, Photooxidation and Photostabilization of Polymers, Wiley, London, 1975. 19 V. SvorEik, R. EndrSt, V. Rybka, V. Hnatowicz and F. Cerny, J. Ejectrochem. Soc., 1994, 141, 582. 20 V. SvorCik, V. Rybka, V. Popok, 0. Jankovskij, I. MiEek and V. Hnatowicz, Eur. Polym. J.,in the press. 21 V. SvorEik, V. Rybka and V. Hnatowicz, to be published. 22 R. Vohra, G. J. Thomson, H. M. Carr, H. Sharma and M. G. Walker, Br. J.Surg., 1991,78,417. Paper 4/03008G; Received 20th May, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500027

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995, 5( l), 31-34 Nanosize Metal Particles in Poly(p-xylylene) Films obtained Low-temperature Codeposition Gleb Sergeev,* Vyacheslav Zagorsky and Marina Petrukhina Department of Chemistry, Moscow State University, 119899 Moscow, Russian Federation A method of preparing polymer materials containing nanometre-scale metal particles has been developed, involving low-temperature techniques. In particular the codeposition of several metal vapours (Mg, Zn, Cd, Pb, Ag) with p-xylylene on surfaces cooled by liquid nitrogen results in the formation of poly( p-xylylene) films containing metal particles that are typically 3-8 nm in diameter. Polymers have been widely used as a matrix for the isolation and fixation of small metal particles.',2 'Nanometre-scale particles' is the most common term for such particles, the sizes of which are < 10 nm.A number of methods of preparing metal-containing polymers have been described,lT2 including cryochemical methods which rely on the fast diffusion of metal vapours towards a cooled surface covered with a thin layer of p01ymer.~ The major goal of these studies is to achieve the uniform distribution of small metal particles in polymer matrices. This problem is currently of importance from both applied and scientific viewpoints, and methods of preparing metal-containing polymer materials which allow one to con- trol the growth of metal particles are therefore of great importance. In this respect, the codeposition of metal vapours with monomers which are themselves able to polymerize at low temperatures and thereby restrict the sizes of growing metal aggregates could be more perspective by comparison with the method described in ref.3. As the monomer we used p-xylylene, which can polymerize at low temperature to form poly( p-xylylene) films which are insoluble in every known organic solvent at room temperature, and are also tough, moisture-resistant and impermeable to most gases and vap~urs.~.~ The low-temperature interaction of chromium vapour with poly( p-xylylene) at the moment of the formation of the latter has been studied previously,6 and it was shown that the metal-polymer films contained both macromolecular n: com-plexes and chromium particles up to 3 nm in diameter in the poly(p-xylylene) matrix.In this study we obtain an initial monomer p-xylylene deposit at 80 K, and then investigate the polymerization process in the presence of metal atoms and small clusters. In principle one can use derivatives of p- xylylene7 or some other monomer polymerized at low tem- peratures (in the presence of initiator-metal vapours) such as acrylamide, acrylonitrile or styrene.8 The purpose of this research is to explore the possibility of synthesizing metal clusters which are < 10 nm in diameter incorporated in a polymer matrix by low-temperature codeposition of metal vapours with p-xylylene followed by subsequent polymerization. In this paper, we concentrate on the synthetic aspects of this technique, on the influence of the experimental conditions on some properties of the metal- polymer films obtained, and explore this approach as a means of preparing poly (p-xylylene) materials which include particles of some relatively easily evaporated binary compounds.Experimental Materials A wide range of metals can be obtained by resistive evapor- ation, followed by vacuum deposition techniques: notably silver, gold, lead and tin, and similar vaporisation techniques were used in this work. All the metals used (Mg, Zn, Cd, Pb, Ag) were of high-purity grade (99.9%) and were employed without further purification. Di-p-xylylene of commercial grade was chromatographically purified. Experimental Apparatus A description of our general experimental apparatus has been given previously.' The apparatus employed in this work was modified by the addition of a quartz tube closed at the bottom end (with an oven over it), which contained both the subli- mation and the cleavage zone for the pyrolysis of the di-p- xylylene (Fig.1). Reactive, monomeric p-xylylene was prepared by pyrolysis of di-p-xylylene at 550-650 "C (Scheme 1). Metal vapours were obtained by resistive heating of the bulk metals over the range 500-1200°C in the same apparatus. The vapours of metal and reactive monomer were code- posited onto a polished copper surface, cooled to 80K by liquid nitrogen under vacuum (typically < mbar). The matrix block was rotated through 180" after deposition and IR spectra were measured over the range 4000-400cm-1 at a series of different temperatures (80-300 K).The temperature of the surface was monitored by a copper-constantan thermocouple. More details of the experimental conditions of this low- temperature codeposition method and the scheme of the vacuum apparatus are presented in a patent." Fig. 1 Schematic representation of the experimental apparatus: 1, quartz tube with metal; 2, quartz tube with di-p-xylylene; 3, quartz tube; 4, polished copper cube; 5, hollow molybdenum screw; 6, KBr window; 7, mirrors; 8, oven for metal evaporation; 9, oven for pyrolysis of di-p-xylylene; 10, oven for evaporation of di-p-xylylene; 11, holder of the reactor in IR spectrometer; 12, copper-constantan thermocouple J.MATER. CHEM., 1995, VOL. 5 Scheme 1 Sample Preparation The period of codeposition of p-xylylene with metal vapours was typically 5-30 min. Subsequently, the metal-p-xylylene matrix was heated slowly (1 K min-') from 80 to 110-150 K and the matrix was exposed to short-wavelength UV irradiation (with a high-pressure Hg lamp) at 80K. Both resulted in the polymerization of p-xylylene (Scheme 1) and aggregation of the metal atoms. As a result, poly(p-xylylene) films including metal particles were obtained and could be extracted from the vessel at room temperature for further investigation. The codeposition of p-xylylene with resistively evaporated compounds such as PbS or ZnS, followed by polymerization yielded poly( p-xylylene) films which included particles of these binary compounds. Furthermore, the controlled addition of dopants with different chemical properties could be explored during the codeposition.Analysis The metal-containing poly( p-xylylene) films were examined with a JEOL JEM-1000 transmission electron microscope (TEM). The particle-size distribution was measured by count- ing several hundreds of particles on the electron micrographs and obtaining mean diameters. The metal content of the films was determined by means of X-ray fluorescent analysis done on a CPM-25 instrument. IR spectra (400-4000 cm-') were recorded on a SPECORD 75 IR. Results An example of globular lead particles isolated in a poly(p- xylylene) matrix is shown in Fig. 2(u). The histogram in Fig.2(b)shows that the sizes of these particles are in the range 3-8 nm with a calculated mean diameter of 5.5 nm. The effect of varying the evaporation temperature of the lead and the di-p-xylylene pyrolysis temperature as well as type of polymerization, on the sizes of the isolated particles is presented in Table 1. Experimental data for the Zn-p-xylylene systems are sum- marized in Table 2. Discussion The method of synthesis of poly(p-xylylene) by pyrolysis of the di-p-xylylene (Scheme 1) used in our work is well known and widely used in industry in isolation coatings in microelec- tronic~.~The pyrolysis of the cyclic dimer di-p-xylylene pro- duces no products other than the reactive monomer p-xylylene (Scheme 1).The polymerization of p-xylylene follows a radical pathway which involves the formation of p-xylylene biradicals, I-= 100 nrn Fig.2 Transmission electron micrograph (a) of the poly( p-xylylene) containing Pb particles (sample no. 5, Table 1) with particle size histogram (b) Table 1 Poly( p-xylylene) film synthesis conditions and average sizes of lead particles Pb mean diameter" (wt .Yo) /nm 1 742 495 - 6.5 5.2 2 600 600 - 0.5 3.4 3 625 630 - 0.1 6.9 4 625 630 + 0.1 7.4 5 735 605 - 1.9 5.5 6 735 605 + 1.9 6.7 a Measured by TEM. Table 2 Poly( p-xylylene) synthesis conditions and average size distri- bution of zinc particles Lap(Zn) qyr(PX) uv Zn mean diameter no. 1°C 1°C irrad. (wt.%) /nm 1 260 630 -4.0 -2 200 520 -0.3 -3 215 530 -0.2 3-8 4 210 530 -0.1 -5 240 490 -10 60-100 followed by dimerisation to yield the biradical dimers, and as a result a linear linked polymer." These experiments involve the codeposition of p-xylylene with metal vapour, and the metal-containing p-xylylene cocondensates are obtained at 80 K.The concurrent pro-cesses taking place during the heating of the matrix are rather complicated and involve primarily the aggregation of J. MATER. CHEM., 1995, VOL. 5 the metal atoms together with polymerization of p-xylylene. These processes have not been studied in detail here. Rather, we have concentrated mainly on the influence of variations in the experimental conditions on the characteristics of the final materials: e.g.the type of polymerization (thermally induced or by UV irradiation), ratio of reagents, temperature of evaporation and pyrolysis, or the temperature of the support. The IR data allow us to monitor the polymerization process at different temperatures and also allowing to obtain additional information. The temperature dependence of the absorbance of some absorption bands is shown in Fig. 3. Curve B (3100 cm-') is associated with CH stretching in the =CH, group in the monomer, and is seen in the spectra at 80 K, while curve A (2850 cm-') is assigned to the symmetric stretching mode of the -CH, -group in poly( p-xylylene).'2 As can be seen from the figure, the polymerization process in the presence of Pb [Fig. 3(b)] starts when the matrix is heated to 120 K, ca.10-20 K below that for pure p-xylylene [Fig. 3(u)]. Note that there are no differences between the IR spectra at 80 K of pure p-xylylene and the lead-containing matrix when lead is present at < 1% by weight. The differences in spectra start to appear when lead is present at several wt.%, and result in a splitting of the strong absorption band of p-xylylene at 875 cm-' (Fig. 4). We assume this new band (at 865 cm-') is due to the oscillations of methylene group of p- xylylene, which forms a weak n-bond with lead atoms or small clusters. A band at 470 cm-' in the chromium system, assigned to a bis-arene complex of chromium,6 was not observed in these Pb-containing systems. The temperature decrease at the beginning of p-xylylene polymerization in the presence of metal, and mentioned before for the lead systems, was characteristic for all metals studied.The explanation could be associated with the interaction of the metal with p-xylylene and the formation of weak low-temperature complexes. Such complexes are believed to make the initiation stage of the polymerization easier. Phenomenologically similar results were obtained for the p-xylylene systems containing silver, cadmium and zinc. In all these cases, the IR data at 80K indicate a weak low-temperature interaction of metal atoms and clusters with p- xylylene (splitting of the 865 cm-' band) which could indicate a rather uniform distribution of metal particles in the poly( p- xylylene) matrix.However, there is no evidence of formation of organometallic compounds in Zn-, Pb-or Ag-p-xylylene matrices or of the bis-arene complexes which were found in the Cr-containing systems6 I 1 I 10 1000 800 600 4 10 Fig. 4 TR spectra obtained after codeposition at 80 K of (a) pure p-xylylene and (b)p-xylylene with Pb vapour In this study, the particles of metals isolated in the polymer matrix appear only to have changed the symmetry of the macromolecules and enhanced certain of the modes in the IR spectra. Among the metals studied in this work, however, mag- nesium was found to be unique. The IR spectra of the magnesium-p-xylylene cocondensates can be explained if one assumes that magnesium and its small clusters react with p-xylylene and are inserted into the polymer chains.Such an insertion reaction is previously known for magnesium atoms and small clusters and is typical in low-temperature codepos- ition re~earch.~~,'~ At 80K new bands at 1210 and 1483cm-' appear in the IR spectra of magnesium-p-xylylene cocondensates (Fig. 5). These bands remain in the spectra up to room temperature and are not observed in pure p-xylylene, poly( p-xylyiene) or in the Zn-, Pb-or Ag-containing systems. The band at 1483 cm-' is similar to the band at 1480 cm-' in p-dichloro- benzene (donor substituent) and may be compared with that in poly(p-xylylene) (1515 cm-'). We believe that this close correlation between the bands can be related to the electron transfer from magnesium to the benzene ring in the mag- nesium-p-xylylene complex.0.30o.*l O.OOL/~80 130 180 230 280 TIK Fig. 3 Temperature dependance of absorption bands in IR spectra: (a)p-xylylene, (b)Pb-p-xylylene (0.1% Pb by weight). Curve A =2850 cm-', -CH,-; curve B=3100cmp1, =CH, The heating of the Mg-p-xylylene cocondensates up to 140-160 K results in the polymerization of the remaining monomers and the appearance of new bands at 720 and 740 cm-' which could be associated with the transformation of a low-temperature rc complex into compounds. As a consequence of these processes, magnesium-p-xylylene com- pounds were fixed in a poly(p-xylylene) matrix up to 300 K in vacuum. The bands (720 and 740 cm-') indicative of the magnesium-p-xylylene interactions immediately disappeared in the presence of air, possible reasons for this being oxidation or hydrolysis.From the TEM data (Table 1) one can see that globular Pb particles of nanometre-scale sizes are isolated in poly(p- xylylene) matrices at room temperature. The particle size is in the range 3-8 nm and is independent of the lead content for 0.1-6.5 wt.% of metal in the films. There is no obvious correlation between the particle size and the reagent evapor- ation and pyrolysis temperatures. The UV irradiation of low-temperature metal-p-xylylene matrices and 'thermally induced' polymerization result in the same lead cluster sizes under otherwise identical experimental conditions (Table 1, nos.3, 4 and 5, 6). It appears that the mobility of the atoms and small clusters is quite high at the moment of polymerization (110-120K) and under irradiation, and this results in the aggregation of particles up to 10nm in spite of any low-temperature rc-complexation. These metallic particles might be accommo- dated in natural holes of the poly(p-xylylene) matrix. So the nature of polymer in this case is the main reason for isolation of definite sizes of particles. The TEM data for the Zn-poly(p-xylylene) films exhibit some differences from the lead materials (Table 2). Globular zinc particles in the same range of 4-10 nm are present in the film at 0.2 wt.% Zn. In addition to these small particles there are higher aggregates up to 100-200 nm.When the Zn content is ca. 10 wt.% in the film, the diameter of the isolated particles is ca. 60-100 nm. There appears to be more cluster aggregation than in Pb-containing polymers. Moreover, the zinc particles are not dispersed so homogeneously within the poly (p-xylyl- ene) matrix. The poly( p-xylylene) used in this work is a typical insulator. The addition of lead up to 10 wt.% results in good insulating characteristics for the materials with isolated metal particles, and a specific resistance as high as 10l6 l2 cm2. The crystalline and metallic nature of these particles in the films has been shown by X-ray studies. Using this technique, new materials Can be prepared either as very thin films deposited on different supports or as self- supporting films having any desired thickness.In addition, the poly(p-xylylene) can be used over a broad range of temperatures (80-450 K), and its tetrafluoro derivatives are even more stable (80-600 K). All these characteristics could provide special fields of application of the poly( p-xylylene) materials with incorporated nanosized metal particles. We have shown, for example, that Ag-containing poly( p-xylylenes) J. MATER. CHEM., 1995, VOL. 5 ~ 2000 1600 1200 800 wavenurnberkm-' Fig. 5 IR spectra obtained after codeposition at 80 K of (a) pure p-xylylene and (b)p-xylylene with Mg vapour (1.5 wt.%) exhibit catalytic activity, in that they catalyse model reactions of the oxidation of methanol. In summary, therefore, we have developed a method for the preparation of polymer materials with nanosized metal particles which is based on the low-temperature codeposition technique.We have shown that this method is applicable to a range of different metals and to some binary compounds such as ZnS and PbS. We gratefully acknowledge Dr. G. V. Byshyeva and Dr. G. M. Zinenkova (Department of Physics, MSU) for obtaining the TEM data, Lab. Chem. Coord. Ligands, INEOC, Rus. Acad. Sci. for the purification of di-p-xylylene. This work was partially supported by ISF (grant number MLSOO) and Russian Fund of Fundamental Investigations (grant number 94-0309987). References 1 M. P. Andrews and G. A. Ozin, Chem. Mater., 1989,1, 174. 2 S. P. Gubin and I. D. Kosobudskii, Russ. Chem. Rev., 1983, 52, 766. 3 G. A. Ozin, J. Mol. Struct., 1980,59, 55. 4 W. F. Gorham, J. Pulym. Sci. A, 1966,43027. 5 M. A. Spivac and G. Ferrante, J. Electrochem. SOC.,1969, 116, 1592. 6 V. A. Sergeev, L. I. Vdovina and A. Yu. Vasilkov, Metaloorg. Chim. (Russian), 1990,3,919. 7 L. Mortillaro, Mater. Plast. Elastumeri, 1966,32,745. 8 G. B. Sergeev and V. A. Batyuk, Cryochemistry, Mir, Moscow, 1986. 9 G. B. Sergeev, V. V. Smirnov and V. V. Zagorsky, J. Organumet. Chem., 1980,201,9. 10 V. V. Zagorsky, M. A. Petrukhina, G. B. Sergeev, V. I. Rozenberg and V. G. Kharitonov, Russ. Patent N5060992/05, 13.10.1992. 11 M. Szwarc, Polym. Eng. Sci., 1976,16,413. 12 S. N. Novikov, I. E. Kardash and A. N. Pravednikov, Visokomolec. Sued. (Russian), 1974,16B, 292. 13 K. J. Klabunde and A. Whetten, J. Am. Chem. Soc., 1986, 108, 6529. 14 V. V. Zagorsky and G. B. Sergeev, Mul. Cryst. Liq.Cryst., 1990, 186. 93. Paper 4/02416H; Received 25th April, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500031

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995,5( l), 35-39 Simple Synthesis of New 2-lmino-4-amino-l,3-dithioles and 2-lmino=4-hydroxy- 1,3=dithioles M. Guillemet," J.M. Raoult F. Pelle,b A. Robert" and M. Baudy-Floc'h*" a Laboratoire de Chimie Structurale, URA CNRS 704, Universite de Rennes I, Campus de Beaulieu, 35042 Rennes Cedex, France Laboratoire de Physico-Chimie des Materiaux, UPR 27 7 CNRS, 7 Place Aristide Briand, 92790 Meudon Bellevue, France A selective reaction of various triethylammonium dithiocarbamates salts with a-a-dicyano epoxides and a-cyano-a- carbethoxy epoxides leads to new 2-imino-4-hydroxy-l,3-dithioles or to new 2-imino-4-amino-l,3-dithioles depending on the experimental conditions. The NLO properties of these dithioles are presented. The discovery of the unusual properties of tetrathiafulvalene (TTF) to behave as an electron donor and to form conducting charge-transfer complexes with various acceptor molecules has stimulated much interest during the past 20 years in the synthesis of a wide variety of TTF analogues.' Significant results have already been obtained by modifications of the TTF framework in order to improve the electroconductive properties.We have recently shown that 4-thioalkyl-5-aryl-2-(p-dimethylaminophenyl)imino-1,3-dithioleswere new unsymmetrical donors of special interest for the two following reasons:2 (i) As observed for the TTF series, these dithioles exhibit two one-electron reversible oxidation waves; (ii) spon- taneous syn-anti isomerism of conjugated imine is observed in solution, allowing the dithiole to adopt the best geometry to fit the strongest intermolecular stabilizing interactions in the solid state. As organization in the solid state is of prime importance for electronic and electrooptic applications, it is also of interest to force such an organization through, for instance, intermolecular hydrogen These considerations prompted us to focus our attention on 2-imino-4-hydroxy-l,3-dithiolesor 2-imino-4-amino- 1,3- dithioles of type A or B: MNH2 wO" sf sKs /N /N A B A preliminary report on the synthesis of type A has recently a~peared,~and as a continuation of this work here we describe in full the preparation of derivatives A as well as the first synthesis of derivatives B and also give results relative to their n-donor ability and their NLO properties. Results 2-Imino-1,3-dithioles 1, 2 and 3 were prepared according to Scheme 1.We have shown that monosubstituted triethylammonium dithiocarbamate salts 6 can selectively attack one cyano group of gem-dicyano epoxides 4 to give new 2-imino-4-amino-5- cyano-1,3-dithioles 1.7 The scope of this reaction is now extended to the epoxides 5. In this case the nucleophile attacks either the cyano group or the ester group of the epoxide 5 according to the experimental procedure and we obtain the 2-imino-4-hydroxy-5-cyano-1,3-dithioles2 or a mixture of 2- imino-4-amino-5-carbethoxy-1,3-dithioles and 2-imino-4-3 hydroxy-5-cyano-1,3-dithioles2 in the proportion of about 70 :30.Thus the 2-imino-4-amino-5-cyano-1,3-dithioles are obtained by reaction of the epoxides 4 and the triethylammon- ium dithiocarbamates 6. The nucleophile attacks the cyano group of epoxide 4 selectively, then the intermediate 7 evolves irreversibly to 8 and then to the dithioles 1 after elimination of one aldehyde molecule. A similar reaction is observed with the epoxides 5 and the triethylammonium dithiocarbamates 6: the nucleophile attacks the nitrile group of the epoxide 5 to give 11, analogous to 7, the evolution of which is strongly related to the reaction conditions. We assume that the dithiocarbamate 6 attacks either the nitrile or the ester group of the epoxide 5. Under non-basic conditions, the attack of the ester group is followed by a quasi-irreversible loss of ethanol to give 9, while the intermediate 11 decomposes into the starting mate- rials 5 and 6 before the epoxide ring opening leads to 12.Under neutral conditions the only products observed are the 2-imino-1,3-dithiafulvenes2 and the aldehyde RCHO. Under basic conditions (NEt,) a mixture of 2-imino-1,3-dithiafulvenes 2 and 3 is obtained (30 :70). Possibly the basic medium favours the deprotonation of 11 and then its irrevers- ible evolution to 12 and 3. This proposed mechanism is in agreement with some work carried out in our laboratory concerning the reaction of epoxide 5 and amidines in which we were able to isolate 13, which is analogous to the intermediate 9 which then evolves by cyclisation and opening of the epoxide to give the imidazole 14 and the aldehyde RCHO, which were fully characterized (Scheme 2).* A similar intermediate was observed during the reaction of epoxide 5 and 2-aminothiazoline.' To the best of our knowledge 1, 2 and 3 are the first 1,3- dithioles bearing either the enaminonitrile, the enolnitrile or the enaminocarbethoxy moieties.Structural assignments of dithioles 1-3 are based on IR, 'H and I3C NMR, UV as well as satisfactory high-resolution mass spectra and elementary analysis. Note that C4 of these derivatives is substituted by a donor group (NH,, OH), while C5 is substituted by a good acceptor (CN, C02Et), such substituents giving rise to a push-pull effect. IR, which shows a nitrile band at 2180-2200 cm-' (cf another cyanodithiole at 2240 cm-' lo), and I3C NMR, with the C4 at low field (154 ppm) and C5 at high field (62 ppm), are in good agreement with this push-pull effect (Experimental).A-Donating Ability Because compounds 1-3 were adsorbed on the electrode (vitreous carbon or Pt) it was not possible to compare their J. MATER. CHEM.. 1995, VOL. 5 + HNEt3 R'NHqs HiEt3 S- 4 6li 6 i H H H' J 11 I 1 CO Et NH R.cHCw" %H$-f Ho' sKs Ho' 'KsN N N 'R' 'R' 'R' -J 0 10 12 cNHNH2 cNHoH+ RCHO + WHO + RCHO SKS sf N N 'R' N'R1 'R' 1 2 3 Scheme 1 Reagents and conditions: i, THF, reflux; ii, THF, NEt,, reflux 5 t NH2 Ph- N= C', Ph \Ph 13 r -\ +RCHOPh-N, +N C I Ph 14 Non-linear Optical Properties Second-harmonic generation (SHG) in the blue is of practical interest." In order to achieve SHG the molecules have to be sufficiently conjugated to present a high dipole moment, then there is the possibility of a large second-order non-linear susceptibility coefficient.However, the incident and second- harmonic radiation must not be absorbed by the material; therefore the corresponding molecules must not be too highly conjugated. We have already shown that 2-(p-dimethylamino-phenyl)imino-l,3-dithiolesare of interest in this field, first because conjugation is not transmitted through the sulfur atoms2 and secondly because spontaneous syn-anti isomerism of conjugated imines allows the correct orientation (using the corona technique) of two quasi-separated dipole moments in the molecule to be achieved in solution and in a polymeric matrix.As a consequence the total dipole moment is quite high even though the molecule in not very conjugated.2 It was also shown that the combination of a benzodithiol group, a long conjugated chain and a series of electron-acceptor groups give compounds that display efficient SHG. In these cases the benzodithiolium cation stabilizes the polar separated state.l23l3 In this context it was of interest to measure the second-order succeptibility coefficient, p, of 1 and 3 which bear cyano-enamino or a carbethoxy-enamino push-pull moieties. The active molecules were dissolved in 1,4-dioxane (10 ml) Scheme 2 cyclic voltammograms with the voltammograms of TTF or other 2-( p-dimethylaminophenyl)imino-1,3-dithioles.2We nevertheless tried to prepare charge-transfer complexes from 1-3, but were unsuccessful.J. MATER. CHEM., 1995, VOL. 5 at a concentration of 10-1-10-3 moll-'. The dipole moments were determined by extrapolation to infinite dilution." The susceptibility was measured as a function of concentration using the wedge Maker fringe technique.'.'' EFISH measurements were performed using the funda- mental frequency provided by a Q-switch Nd:YAG laser operating at 1.06 pm at a repetition rate of 80 Hz. Vertical polarization of the laser beam was achieved by using a Glan polarizer. High-voltage dc pulses (up to 50 kV cm-') were applied synchronuously with the optical pulses.The second harmonic, separated from the fundamental frequency by an appropriate set of filters, was detected by a 56TVP photomul- tiplier. For each translation of the cell, the signal was averaged 32 or 64 times by an IEEE interfaced fast digitizer (7912AD- Tektronix). The cell translation was driven by a computer which was also used for data acquisition and processing. Each experiment was calibrated relative to a wedge quartz plate with the same geometry as the liquid cell. The temperature of the solution was controlled during the experiment. Least- squares fits of the concentration dependence of the second- harmonic intensity, normalized to the second-harmonic intensity of the reference, provided the magnitude of the macroscopic coefficient To.At the low concentrations used, the interaction between molecules can be neglected and the magnitude of the molecular hyperpolarizability, y, was calcu- lated from To after substracting the contribution of the solvent. The combined influence on a solution of an optical laser field E" and of a static field IF' resulting from an applied dc voltage induces a microscopic polarisation: Pizw= pijk +yijkl Ej" EkWElo,where pijk is the molecular second-order non-linear optical susceptibility and Yijkr is the molecular third-order hyperpolarisability. For a pure liquid, the macroscopic susceptibility l-,,,, is related to the mean microscopic hyperpolarisability coefficient yxxxx:~xxxx=NJ;J,,,, =Nfyo,where N is the number of mol- ecules per unit volume of the liquid andfthe local field factor in the Lorentz approximation. f=(fW)2f2"fo For a polar liquid : yo =ye +p,(p)2/5kT Moreover, for molecules with strong electron-withdrawing substituents, 7" is negligible. We then use : yo =pp/5kT, where p is the dipole moment of the molecule in Dt and is in lo-,' cm5 D esu-'.Results Results are presented in Table 1. Owing to the important dipole moment of 3 [R' =C6H4N( Me),, C6H40CH3] its second-order hyperpolarisability is low compared to that of 3 (R' =C6H4CH3), which is similar to those of 4-nitroaniline (Po=9) and NJV-dimethy1-4-nitroaniline (Po=12).14 In conclusion, in this paper we report the first synthesis of a series of new 2-imino-1,3-dithioles bearing substituents that have intermolecular hydrogen bonds.The importance of these compounds could be recognized in several fields, particularly D (Debye)= 3.33564 x lop3'C m. 37 in view of their close relationship to 4-cyano-5-aminoimida- zoles and 4-carboethoxy-5-aminoimidazolesand the synthesis of purines,15 and also as precursors of tetrathiafu1venesl6 and extended tetrathiafulvenes. In addition, we have determined the non-linear hyperpolarizability of the molecules, which is similar to those found for 4-nitroaniline or N,N-dimethyl-4- nitroaniline. Experimental 'H NMR spectra were recorded at 80 MHz on Bruker WP 80 spectrometer and 13C NMR spectra at 75 MHz on Bruker AM 300 spectrometer with tetramethylsilane as internal refer- ence.Mass spectra were determined with a Varian Mat 3 11 spectrometer. IR spectra were determined with a Perkin-Elmer 225 or 1420 spectrometer. Melting points were meas- ured with a Kofler hot-stage apparatus. 2-Imino-4-amino-9cyano-l,3-dithioles (1) A solution of gem-dicyanoepoxide 417 (5 mmol) in tetrahydro- furan (THF; 25 ml) was added slowly to a suspension of a triethylammonium dithiocarbamate salt 618 (5 mmol) and refluxed for t h depending on the R' substituents. The mixture was poured into water and extracted with ether 2 x 200 ml. The extracts were dried (Na,SO,) and evaporated. The residue was worked up with ethanol to give the dithiole 1 as a precipitate, which was recrystallized from ethanol. 1 (R' =p-C1C6H4, t =2 h; 46%); mp 260 "C.Found: C, 45.2; H, 2.18; N, 15.62; S, 13.21; C1, 23.69% (M', 267.7625); CloH,6N&C1 requires: C, 44.9; H, 2.26; N, 15.7; S, 13.24; C1, 23.9% (M', 267.7575). v,,,(Nujol)/cm-': 3400-3100 br (NH); 2200 s (CN); 1630 s (C=N). 6, (CDCl,-CF,CO,H): 7.20 (4 H, m, C6H4). Amax (EtOH)/nm (&max/lmol-' cm-'):249 (26700); 356 (20000). 6, (CDC1,-CF,CO,H): 62 (s, C'); 113 (s, CN); 130 (dd, Ar); 131 (dd, Ar); 132 (t, Ar); 138 (t, Ar); 154 (s, C4); 189 (s, C2). 1 (R'=p-MeC6H4, t=2 h; 50%); mp 174°C. Found: C, 53.64; H, 3.64; N, 16.88; S, 25.84%. C,,H1,N,S, requires: C, 53.44; H, 3.66; N, 17.00; S, 25.9%, v,,, (Nujol)/cm-' :3300-3000 br (NH), 2200 s (CN); 1625 s (C=N). Amax (EtOH)/nm (cmaX/l mol-' cm-'): 229 (18000).6H (CDC1,-CF3C02H): 7.10 (4 H, m, C6H4); 2.32 (3 H, S, CH3). 6, (CDCl,-CF,CO,H):21.4 (9, CH3); 61.9 (s, C5); 112.7 (s, CN); 128.3 (dd, Ar); 129.4 (m, Ar); 131.4 (dd, Ar); 131.7 (t, Ar); 152.7 (s, C4); 187.9 (s, C'). 1 (R'=p-MeOC6H4, t=3h; 55%); mp 188°C. Found: C, 50.25; H, 3.45; N, 16.04; S, 24.23% (M' 263.0197). CllHI9N30S2 requires: C, 50.19; H, 3.42; N, 15.96; S, 24.33% (M+ 263.0187). v,,,(Nujol)/cm-' :3400-3100 br (NH); 2200 s (CN); 1630 s (C=N); A,,,(EtOH)/nm (~~~~/l mol-' cm-') 250 (45000). dH (CDCl,-CF,CO,H): 7.12 (4 H, m, C6H4); 3.80 (3 H, s, OCH,). 6, (CDC1,-CF,CO,H): 55.7 (s, OCH,); 76.9 (s, C5); 116.2 (dd, Ar); 124.9 (dd, Ar); 125.8 (s, Ar); 104.2 (s, CN); 154.2 (s, C4); 188.4 (s, C').1 (R'=C6H5, t=12 h; 43%); mp >260°C. Found: C, 51.21; Table 1 Physical data for dithioles 1 and 3 3,,,/nm (log 611 mol-' cm-') PI1 lop3' cm5 D esu-' PD PI cm5 esu-' 1 R' =C,H,N( Me), 3 R' =C,H,N( Me)* 270 (4.2) 269 (4.39) 2 25 1.83 13.8 1.1 1.8 3 R' =C,H40CH3 359 (4.30) 256 (4.07) 18-21 14.7 1.2-1.4 3 R' =C,H4CH3 358 (4.14) 255 (4.05) 11-14 1.03 10.7- 13.6 38 H, 3.06; N, 18.15; S, 27.58%. CloH1,N,S, requires: C, 51.21; H, 3.00; N, 18.02; S, 27.46%.v,, (Nujol)/cm-' 3400-3100 br (NH); 2200 s (CN); 1625 s (C=N). A,,, (EtOH)/nm (&,,,/l mol-' cm-') 253 (22000). 6, (CDCl3-CF3CO,H): 7.32 (5 H, m, C6H5)-1 [R'=p-N(CH,),C,H,, t=6 h; 80%]; mp 210°C. Found: C, 52.17; H, 4.34; N, 20.29; S, 23.18%. C13H12N4S2 requires: C, 51.96; H, 4.26; N, 20.19; S, 23.59%. vmax (Nujol)/cm-':3300-3100 br (NH); 2190 s (CN); 1630 s (C=N).l,,,(EtOH)/nm (cmax/l mol-' cm-') 270 (16200). 6, (CDC1,-CF,CO,H): 7.22 (4 H, m, C6H4); 2.92 (6 H, s, CH,). hc (CDCl,): 40.3 (4, CH,); 65.8 (s, C5); 112.03 (s, CN); 112.32 (dd, Ar); 126.67 (dd, Ar); 129.8 (s, Ar); 138.5 (s, Ar) 149.5 (s, C'); 187.8 (s, C'). 1 (R1=p-CH3C6H4SO2NH,t= 1 h; 32%); oil. Found: C, 40.98; H, 2.89; N, 17.23; S, 30.02%. CllH10N4S302 requires : C, 40.49; H, 3.07; N, 17.18; S, 29.45%. ~,,~(Nujol)/cm-~: 3380-3120 br (NH); 2200 s (CN); 1625 s (C=N); ~,,,(EtOH)/nm (cmax/l mol cm-l) 246 (28000). 6, (CDC1,-CF,CO,H): 7.50 (4 H, m, C,H,); 2.48 (3 H, s, CH,). 1 [R' =N(Me),, t=4 h; 52%); mp 208 "C. Found: C, 35.83; H, 3.96; N, 28.10; S, 32.11%.C6H,N,S, requires: C, 36.0; H, 4.0; N, 28.0; S, 32.0%. vmax(Nujol)/cm-': 3400-3100 br (NH); 2200 s (CN); 1625 s (C=N). A,,,(EtOH)/nm (hax/l mol cm-') 244 (31000). 6, (CDCl,-CF,CO,H): 3.17 (6 H, s, CH3). 2-Imino-4-hydroxy-5-cyano-1,3-dithioles(2) Triethylammonium dithiocarbamate salt 6 (5 mmol) was added to a solution of a-cyano-a-carboethoxyepoxide5" (5 mmol) in THF (40 ml). The solution was refluxed for t h depending on the substituent R. The cooled mixture was diluted with water and extracted with ether (2 x 100 ml). The extracts were dried (Na,S04) and the solvent evaporated. The residue was worked up with ether to yield the dithiole 2 as a precipitate which was filtered off and recrystallized from ethanol.2 (R'=p-ClC,H,, t=24 h; 40%), mp 197 "C. Found: C, 44.69; H, 1.86; N, 10.42; S, 13.21; C1, 23.83% (M+ 268.74). CloH5N2S20Cl requires : C, 44.65; H, 2.05; N, 10.51; S, 13.21; C1, 23.80% (M+ 268.745). v,,, (Nujol)/cm-': 3300-3100 br (OH); 2200 s (CN). A,,, (EtOH)/nm (&,,,/l mol-' cm-') 260 (21000). 6, (CDCl,-CF,CO,H): 7.20 (4H, m, Ar). 6, (CDC1,-CF,CO,H): 77.2 (s, C'); 112.9 (s, CN); 127.8 (dd, Ar); 130.7 (dd, Ar); 133.07 (t, Ar); 136.1 (t, Ar); 136.05 (s, C4); 172.9 (s, C2). 2 (R' =p-CH,C,H,, t =8 h; 33%); mp 204 "C. Found : C, 53.22; H, 3.22; N, 11.29; S, 25.80%. C,,H,N,S,O requires: C, 53.15; H, 3.26; N, 11.30; S, 25.62%. v,,,(Nujol)/cm-l : 3300-3100 br (OH); 2200 s (CN). A,,,(EtOH)/nm (cmJ mol-' cm-') 248 (32000). 6, (CDC1,-CF3C02H) : 7.22 (4 H, m, Ar); 2.35 (3 H, s, Me).2 ( R1 =p-CH30C6H4, t =24 h; 70%); mp 192 "C. Found C, 50.00; H, 3.03; N, 10.60; S, 24.24%. C,,H,N,S,O, requires: C, 49.85; H, 3.12; N, 10.48; S, 24.32%. ~,,,(Nujol)/cm-~: 3320-3200 br (OH); 2205 s (CN). A,,,(EtOH)/nm (cmax/l mol cm-'): 250 (45000). 6, (CDC1,-CF3C02H): 7.12 (4 H, m, Ar); 3.75 (3 H, s, OMe). 2 [R'=p-N(cH3),C6H4, t=6 h; 65%; mp 192°C. Found C, 51.98; H, 3.97; N, 15.16, S, 23.10%. C,,H,,N,S,O requires : C, 52.08; H, 3.95; N, 15.26; S, 23.05%. v,,,(Nujol)/cm-': 3300-3100 br (OH); 2205 s (CN). A,,,(EtOH)/nm (&,,,/l mol-' cm-'): 270 (16200). 8, (CDC13-CF3C02H): 7.17 (4 H, m, Ar); 2.95 (6 H, s, Me). 2 [R'=N(CH,),, t=24h; 60%]; mp 154°C. Found C, 35.82; H, 3.48; N, 20.89; S, 31.84%.C6H7N30S2 requires: C, 35.61; H, 3.52; N, 20.93; S, 31.81%. vrnax(Nujol)/cm-': J. MATER. CHEM., 1995, VOL. 5 3300-3100 br (OH); 2190 s (CN). A,,,(EtOH)/nm (cmaX/lmol-' cm-') 244 (31000). 6, (CDCl,-CF,CO,H): 2.62 (6 H, S, CH3). 6, (CDCl,-CF,CO,H): 40.56 (9, CH3); 77.2 (s, C'); 112.67 (s, CN); 127.33 (s, C4); 181.22 (s, C2). n2 (R'=N-0 t= 8 h; 50%); mp 158 "C. Found, C, 39.49; H, 3.72; N, 17.27;S, 26.35%. C,HloN,02S, requires : C, 39.50; H, 3.73; N, 17.57; S, 26.25%. v,,, (Nujol)/crn-': 3210-3120 br (OH); 2200 s (CN). A,,(EtOH)/nm (cmax/l mol-' cm-I): 240 (18000). 6, (CDC13): 6.45 (1 H, S, OH); 3.82 (4 H, t, OCH,); 2.97 (4 H, t, NCH,). 6~ (CDC1,-C&6): 56.06 (tt, NCH,); 66.78 (tt, OCH,); 83.44 (s, C5); 114.7 (s, CN); 125.32 (s, C4).2-Imino-4-amino-5-carbethoxy-1,3-dithioles(3) To a mixture of a-cyano-a-carboethoxy epoxide 5 (5 mmol) and triethylammonium dithiocarbamate salt 6 (5 mmol) was added trimethylamine ( 15 mmol) and acetonitrile (50 ml). The solution was refluxed for t h. Then the solvent was removed under reduced pressure and the residue was treated in two different ways: (a) work up with ethanol yielded the dithiole 3 as a precipitate. Evaporation of the filtrate lead to the dithiole 2 by treatment with ether. (b)Column chromatogra- phy on silica gel with ether-petroleum ether (30: 70) as eluent gave first the aldehyde, then the dithiole 3 and lastly the dithiole 2.3 was recrystallized from ethanol. 3 [R' =p-ClC6H,; t =24 h; treatment (a);40%]; mp 244 "C.Found: C, 45.78; H, 3.5; N, 8.9; S, 20.36; C1, 11.28% (M' 313.996). C1,H,,N,O,S,C1 requires : C, 46.09; H, 3.61; N, 8.70; S, 20.34; C1, 11.26% (M' 313.9950). v,,,(Nujol)/cm-' : 3400-3100br (NH); 1670s (CO); 1615s (C=N). A,,, (EtOH)/nm (&,,,/l mol-' cm-l) 255,358 (11400, 12000). 6, (CDCI,): 7.45 (4 H, m, Ar); 5.60 (2 H, s, NH,); 4.26 (2 H, q, CH,); 1.32 (3 H, t, CH3). 6c (CDCl,): 14.45 (qt, CH3); 60.84 (tq, CH,); 126.5 (s, C4); 132.8 (s, Ar); 130.07 (dd, Ar); 131 (dd, Ar); 137.1 (s, Ar); 150.7 (s, C'); 163 (s, CO); 188.4 (s, C'). 3 [R'=3,5-di-ClC,H3; t= 18 h; treatment (a); 50%]; mp 226°C. Found: C, 41.63; H, 2.62; N, 7.93; S, 18.33; C1, 20.45 (M' 347.959). C12HloN20,S2C1, requires: C, 41.26; H, 2.86 N, 8.02; S, 18.30; C1, 20.34% (M', 347.9560).v,,, (Nujol)/cm-': 3300-3100 br (NH); 1670 s (CO); 1615 s (C=N). 6, (CDCl,): 7.30 (3 H, m, Ar); 5.65 (2 H, s, NH,); 4.27 (2 H, q, CH,); 1.32 (3 H, t, CH,). 3 [R' =3-NO2C,H,; t = 18 h; treatment (a); 50%]; mp 234°C. Found: C, 44.35; H, 3.43; N, 12.82; S, 19.55% (M' 325.0184). Cl,H,lN,S,O, requires: C, 44.29; H, 3.41; N, 12.91; S, 19.71YO(M' 325.0190). vmax(Nujol)/cm-': 3400-3200 br (NH); 1670 s (CO); 1620 s (C=N). 6, (CDCl,): 8.08 (4 H, m, Ar); 5.62 (2 H, s, NH,); 4.32 (2 H, q, CH,); 1.32 (3 H, t, CH,). 3 [R'=p-MeC&; t= 12 h; treatment (b);50%]; mp 190°C. Found: C, 53.27; H, 4.69; N, 9.36; S, 21.77% (M', 294.049). CI3Hl4N2O2S2requires: C, 53.03; H, 4.79; N, 9.51; S, 21.78% (M' , 294.0509). vmaX(Nujol)/cm-': 3450-3280 br (NH); 1680 s (CO); 1615 s (C=N).8, (CDCl,): 7.29 (4 H, m, Ar); 5.68 (2 H, s, NH,); 4.27 (2H, q, CH,); 2.45 (3 H, s, CH,); 1.30 (3 H, t, CH,). 6, (CDC1,): 14.5 (qt, CH,CH,); 21.5 (4, CH,); 60.57 (tq, CH,); 125.5 (s, C4); 128.5 (dd, Ar); 129.09 (s, Ar); 129.46 (s, Ar); 131.26 (dq, Ar); 151.9 (s, C'); 162.4 (s, CO); 188.7 (s, C2). 3 [R1=p-CH30C6H4, t=12 h; treatment (b); 40%] mp 184°C. Found: C, 50.30; H, 4.51; N, 9.15; S, 20.45%. C1,Hl,N2S20, requires: C, 50.29; H, 4.54; N, 9.02; S, 20.66%. v,,,(NuJol)/cm-': 3320-3250 br (NH); 1660 s (CO); 1615 s (C=N). A,,,(EtOH) nm (cmax/l mol-I cm-') 359; 259 (20000; 25000). 6, (CDCl,): 7.16 (4 H, m, Ar); 5.68 (2 H, S, NH,); 4.27 (2 H, q, CH,); 3.87 (3 H, s, OCH,); 1.35 (3 H, t, CH,).6, (CDCl,): 14.48 (qt, CH,); 55.61 (9, OCH,); 60.6 (tq, CH,); J. MATER. CHEM., 1995, VOL. 5 115.8 (dd, Ar); 129.7 (dd, Ar); 126.6 (s, C'); 127.6 (s, Ar); 151.4 (s, C5); 160.9 (s, Ar); 162.3 (s, CO); 188.8 (s, C'). 3 [R1=C6H5, t=16h; treatment (b), 30%] mp 218°C. Found: C, 51.52; H, 4.33; N, 10.05; S, 20.65%. C12H12N2S202 requires: C, 51.40; H, 4.31; N, 9.99; S, 22.87%. v,,, (Nujol)/cm-': 3450-3290 br (NH); 1665 s (CO); 1615 s (C=N). 6, (CDCl,): 7.45 (5 H, m, Ar); 5.61 (2 H, S, NH,); 4.30 (2 H, q, CH,); 1.35 (3 H, t, CH,). 6, (CDC1,): 14.52 (qt, CH,); 60.78 (tq, CH,); 124.8 (s, C4); 128.63 (d, Ar); 130.70 (d, Ar); 130.88 (d, Ar); 134.56 (s, Ar); 152.1 (s, C5); 163.4 (s, CO); 189.7 (s, C'). 3 [R1 =p-N(CH3),C6H4, t= 12 h, treatment (b);31%]; mp 194°C.Found: C, 51.88; H, 5.06; N, 12.76; S, 19.96%. C14H17N3S202requires: C, 51.96; H, 5.29; N, 12.99; S, 19.82%. vmax(Nujol)/cm-': 3420-3210 br (NH); 1650 s (CO); 1610 s (C=N). A,,,(EtOH) nm (~,~,/lmol-' cm-') 269; 359 (25000; 20000). 6, (CDCI,) 7.15 (4 H, m, Ar); 5.66 (2 H, s, NH,); 4.25 (2 H, 4, CH,); 3.00 [6 H, S, N(CH3)]; 1.30(t, 3 H, CH,-CH,). 6, (CDCl,): 14.5 (qt, CH,CH3); 40.2 [q, N(CH,),]; 60.5 (tq, CH2-CH,); 121.7 (s, Ar); 121.9 (s, Ar); 112.7 (dd, Ar); 128.9 (dd, Ar); 121.8 (s, C4); 151.9 (s, C5); 162.4 (s, CO); 189.1 (s, C2). 3 [R1=p-CH,C,H,SO,NH, t= 1 h, treatment (b);42%]; mp 186°C. Found: C, 41.72; H, 3.78; N, 11.46; S, 26.12%. C13H15N304S, requires: C, 41.82; H, 4.02; N, 11.26; S, 25.74%. v,,,(Nujol)/cm-': 3460-3200 br (NH); 1680 s (CO); 1620 s (C=N).BH (CDCI,): 7.48 (4 H, m, Ar); 5.57 (2 H, s, NH,); 4.30(2 H,q,CH2);2.47(3H,s,CH,); 1.32(3 H, t,CH,-CH,). 6, (CDCl,): 13.69 (qt, CH,-CH,); 21.47 (9, CH3); 62.58 (tq, CH,-CH,); 129.07 (dd, Ar); 129.08 (s, C'); 130.38 (dd, Ar); 131.51 (s, Ar); 147.70 (s, Ar); 150.99 (s, C5); 163.70 (s, CO); 184.65 (s, C'). 3[R'=CH3,t=2 h;treatment(b);38%];mp 170"C.Found: C, 38.51; H, 4.53; N, 12.74;S, 29.40%. C,HIoN2S2O2 requires: C, 38.53; H, 4.58; N, 12.84; S, 29.35%. vmax(Nujol)/cm-': 3400-3305 br (NH); 1660 s (CO); 1615 s (C=N) cm-l. dH (CDCI,-CF,CO,H): 4.30 (2 H, 9, CH2); 3.65 (3 H, S, CH3); 39 1.35 (3 H, t, CHZ-CH,). dc (CDCl3-CFjC02H): 14.18 (qt, CH,-CH,); 32.5 (9, N-CH3); 62.28 (tq, CHZ-CH,); 121.9 (s, C'); 152.7 (s, C5); 163.8 (s, CO); 187.4 (s, C').References 1 M. Narita and C. U. Pittman, Synthesis, 1976, 489; A. Krief, Tetrahedron, 1986, 42, 1209; G. Schukat, A. M. Richter and E. Fanghanel, SuIfur Rep., 1987,7,155. 2 D. Lorcy, A. Robert, S. Triki, L. Ouahab, P. Robin and E. Chastaing, Tetrahedron Lett., 1992,33, 7341. 3 Nonlinear Optical Properties of Organic Molecules and Crystals, ed. D. S. Chemla and J. Zyss, Academic Press, New York, 1987. 4 Ph. Blanchard, M. Salle, G. Duguay, M. Jubault and A. Gorgues, Tetrahedron Lett., 1992,33,2685. 5 J.M. Fabre, J. Garin and S. Uriel, Tetrahedron, 1992,48, 3983. 6 M. R. Bryce, Chem. SOC.Rev., 1991,20,355. 7 M. Guillemet, M. Baudy-Floc'h and A. Robert, J. Chem. SOC., Chem. Commun., 1991,906. 8 M. Guillemet, Thesis, Rennes, 1992. 9 S. Jaguelin, A. Robert and P. Gayral, Eur. J. Med. Chem., 1991, 26, 51. 10 M. G. Miles, J. S. Wager, J. D. Wilson and A. R. Siedle, J. Org. Chem., 1975,40,2577. 11 K. D. Singer and A. F. Garito, J. Chem. Phys., 1981,75,3572. 12 M. Blanchard-Desce, I. Ledoux, J. M. Lehn, J. Malthete and J. Zyss, J. Chem. SOC., Chem. Commun., 1988,737. 13 S. Palacin, M. Blanchard-Desce, J. M. Lehn and A. Barraud, Thin Solid Films, 1989, 178, 387. 14 K. D. Singer, J. E. Sohn, L. A. King and H. M. Gordon, J. Opt. SOC. Am. B, 1989,6,1339. 15 R. Comper, H. Gand and F. Faygin, Tetrahedron, 1966,1885. 16 S. Bittner, A. Moradpour and P. Krief, Synthesis, 1989, 132. 17 M. Baudy, A. Robert and A. Foucaud, J. Org. Chem., 1978, 43, 3732. 18 J. E. Hodgkins and W. Preston Reeves, J. Org. Chem., 1964, 29, 3098. 19 A. Robert and A. Foucaud, Bull. SOC. Chim. Fr., 1969,2531. Paper 4/05638H; Received 31st May, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500035

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995, 5(l), 41-46 Two-dimensional Ferromagnetic Intermolecular Interactions in Crystals of the p-Cyanophenyl Nitronyl Nitroxidet Radical Yuko Hosokoshi, Masafumi Tamura, Hiroshi Sawa, Reizo Kato and Minoru Kinoshita* Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106,Japan The crystal structure of the p-cyanophenyl nitronyl nitroxide [2-(4-cyanophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-1 -oxyl 3-N-oxide, abbreviated as p-CNPNN] radical has been solved. It belongs to the orthorhombic system, space group k2a, with a=10.482(2) A, b =26.61 5(5)A, c =9.903(2) A and Z= 8. The asymmetric unit contains two independent radical molecules. The intermolecular contacts between the cyano phenyl groups and the nitroxide groups form a quasi-square lattice.The magnetic susceptibility has been measured in the temperature range 1.8-300 K. The temperature dependence of the paramagnetic susceptibility above 4 K can be explained by the ferromagnetic square- lattice Heisenberg model with J/kB=0.75 K. Two-dimensionality of the crystal is also confirmed by single-crystal electron paramagnetic resonance (EPR) spectra. During the last three years, remarkable progress has been made in the research of magnetism in organic molecular crystals.' Some genuine organic ferromagnets have been found2p4 since the first organic ferromagnet P-p-NPNN (P-p-nitrophenyl nitronyl nitroxide) was discovered in 1991.5,6 However, the detailed mechanism of the ferromagnetic inter- molecular interactions in these materials remains the subject of active experimental and theoretical research.Further under- standing of the origin of the ferromagnetic interactions is desired to improve the rational design of molecular magnets in terms of molecular and crystal structures. In order to draw out the physics behind the magnetism in molecular materials, a knowledge of the relationship between the molecular packing and the intermolecular magnetic interactions is of primary importance. In a previous paper,7 we have reported on p-fluorophenyl nitronyl nitroxide (p-FPNN), which forms a 3D network of ferromagnetic intermolecular interactions. Our purpose is to survey the relationship between molecular form, crystal struc- ture and magnetism in a series of substituted phenyl nitronyl nitroxide radical crystals. By classifying the molecular packing of these compounds in the crystals, useful knowledge for the control of magnetism is expected to be found.In this paper, we report on p-cyanophenyl nitronyl nitroxide (p-CNPNN), which has an electron-attracting substituent at the para pos-ition, similar to the cases for p-NPNN and p-FPNN. We first describe the crystal structure of this compound with emphasis on its sheet structure. The temperature dependence of the paramagnetic susceptibility is analysed in terms of the ferro- magnetic square-lattice model of the Heisenberg spin system. Paying attention to the interactions between the nitroxide group and the phenyl ring, the origin of the magnetic two- dimensionality of p-CNPNN is discussed.The role of the cyano group in the crystal is briefly considered from the electrostatic viewpoint. Experimental Sample Preparation The synthetic procedure was described The precur- sor of the p-CNPNN radical, the anhydrous adduct of p-cyanobenzaldehyde and 2,3-bis (hydroxylamino)-2,3-dimethyl-butane, could not be isolated from the reaction mixture in methanol. Instead, we refluxed a solution in benzene of p- ?The use of the term 'nitroxide' is discouraged by IUPAC; the preferred term is 'aminoxyl'. cyanobenzaldehyde and 2,3-bis( hydroxylamino)-2,3-dimethyl-butane for 1h. The red insoluble tar-like reactant was removed by decantation. Concentration of the supernatant yielded a yellow-white solid (yield 7%), which was readily oxidized to p-CNPNN by lead dioxide. The single crystals were obtained by slow evaporation of concentrated benzene solutions at room temperature.UV-VIS Spectra The UV-VIS spectrum of an ethanolic solution of p-CNPNN was measured using a Hitachi 556 Spectrophotometer. For comparison, we also measured the spectra of an ethan-olic solution C(7.0-8.8) x mol dm-3] of PNN (phenyl nitronyl nitroxide), p-FPNN and p-NPNN. X-Ray Crystallographic Analysis X-Ray intensity data at 298 K were collected on a MAC Science automated four-circle diffractometer with graphite- monochromated Mo-Ka radiation up to 28 =60". Unit-cell parameters were determined from the least-squares refinement for 20 reflections within 20 <28/degrees <33.1055 indepen- dent reflections with IFo[>40(lF01) were used for structural analysis. The structure was solved by direct methods and refined by the full-matrix least-squares procedure using the anisotropic approximation for non-hydrogen atoms. Analytical absorption corrections were performed." All the procedure were carried out using the 'Crystan' program package of MAC Science. Static Magnetic Measurements The magnetization below 10 K for the field up to 55 kOe and the susceptibility from 1.8 to 300K were measured using a Quantum Design MPMS SQUID magnetometer. The suscep- tibility below 10 K was measured under the small applied field (500 Oe) to avoid saturation effects as far as possible.The field was applied parallel to the b axis. The diamagnetic contribution was estimated to be -1.30 x emu mol-' (-1.64 x m3 mol-') from fitting the data above 200 K to the Curie law. EPR Measurements EPR spectra of single crystals were measured at 293 K using a JEOL JES-FElXG EPR spectrometer (X band), rotating the crystal around the crystallographic axes. Results UV-VIS Spectra The UV-VIS absorption spectrum of p-CNPNN was com- pared with those of PNN, p-FPNN and p-NPNN (Table 1). The common feature is the three absorption bands around 590, 360 and 260 nm. Ullman et aL8 assigned these bands to the n-n*, n-n* and intramolecular charge-transfer (CT) trans- itions, respectively. The low-energy shifts of the n-n* and intramolecular CT bands can be seen in p-NPNN'' and p-CNPNN, suggesting greater delocalization of the unpaired n-electron in these compounds, i.e.bathochromic effects. This can be related to the electron-withdrawing nature of the para- substituents, which may be important when we consider the molecular packing in the crystal in view of the charge distribution over each molecule. Crystal Structure Crystallographic data and the final positional parameters are summarized in Tables 2 and 3. The thermal parameters of two methyl carbon atoms, C(9) and C(10), are large owing to thermal vibration or structural disorder. Because of this, the convergence of the structure refinement is not very satisfac- tory (the final Rfactor is 9.2%), and it is meaningless to refine the atomic parameters for the hydrogen atoms on such methyl carbon atoms.There are two crystallographically independent molecules (A and B). The long axes of both molecules are on the crystallographic twofold rotation axes. Fig. 1 shows an ORTEP12 drawing of the A and B molecules. No marked difference in bond lengths and angles is observed between the A and B molecules. However, the dihedral angles between the best planes of the ONCNO moieties and phenyl rings of the A and B molecules are 18.4 and 35.9", respectively. Fig. 2 and 3 display the molecular packing in the crystal viewed along the b and c axes. The sheet structure spread over the ac plane is outstanding. The adjacent sheets are Table 1 Absorption maxima of the UV-VIS spectra of PNN, p-FPNN, p-CNPNN, p-NPNN in ethanol sample 1Jnm PNN 588 362 264 p-FPNN 590 360 263 p-CNPNN 592 378 288 p-NPNN 592 392 315 Table 2 Crystallographic data of p-CNPNN C14H1f5N302 formula weight 258.30 crystal sizefmm 0.51 x 0.38 x 0.20 crystal system orthorhombic space group Zc2a VIP 2762.6( 9) 10.482( 2) bJ+ 26.615(5) CIA 9.903 (2) Z 8 D,Jg cmP3 1.24 radiation Mo-KR (1=0.71073 A)total reflections measured 2338 unique reflections 2060 reflections used (IFo/>4a((F01)) 1055 residuals: R; R," 0.092; 0.095 goodness of fit: S 2.38 'The function minimized was sum [~(lF~l~-lF,1~)~],in which w =[(olFoI)Z] -* .J. MATER. CHEM., 1995, VOL. 5 Table 3 Positional parameters and equivalent isotropic thermal parameters of p-CNPNN with standard deviations in parentheses' atom X Y Z BW -0.1297(9) -0.0594( 9) 0 0 -0.037( 1) -0.036( 1) 0 -0.029(2) -0.107( 1) 0.137( 2) 0 0 -0.07( 1) -0.06( 1) 0.17516 0.161 3( 4) 0.1916( 7) 0.2463( 6) 0.2730( 5) 0.3250(5) 0.351 1( 6) 0.1075 (5) 0.0727(5) 0.1011(7) 0.4053( 7) 0.4483 (6) 0.253(4) 0.343 (4) 0.186( 1) 0.0901 (9) 0 0 0.115(1) 0.113( 1) 0 0.060( 1) 0.138( 1) 0.134( 2) 0 0 0.20( 1) 0.19(1) 9.0(4) 4.6( 3) 3.2( 3) 5.8(4) 3.8(4) 8.7(6) 5.9(4) 13.0(8) 4.5(5) 6.0( 5) 3.5(4) 544) 0.3050( 7) 0.4055( 7) 0.5 0.5 0.387( 1) 0.386(2) 0.5 0.4265(8) 0.352( 1) 0.382( 1) 0.5 0.5 0.29( 1) 0.26(1) 0.34( 1) 0.38( 1) 0.29( 1) 0.43(1) 0.3 1 ( 1) 0.41 (1) 0.3752( 4) 0.3897( 4) 0.3607( 6) 0.3057( 7) 0.2803( 5) 0.2266( 5) 0.2026( 7) 0.4443( 5) 0.4524( 6 0.4776( 6 0.1470(8 0.1053(8 0.307(5) 0.098 (5) 0.499( 6) 0.484( 7) 0.456( 6) 0.473(5) 0.480( 6) 0.5 15( 5) 0.1082( 8) 0.0480(8) 0 0 -0.014( 1) -0.017( 2) 0 0.0108( 9) 0.1254 1 ) 0 0 -0.117(2) -0.04( 1) -0.04(2) -0.15( 2) -0.12( 1) -0.1 1 (2) O.ll(1) 0.10( 1) 0.23(1) 5.2(2) 3.6( 2) 3.3(4) 4.5(4) 6.3 (4) 8.0(5) 6.5(6) 3.0( 2) 6.0(4) 8.4(8) 11.9(9) 4.7(3) " The positional parameters of the hydrogen atoms on C(9) and C( 10) were not refined for the reason mentioned in the text.related by b glide reflection symmetry. Within the sheet, each A molecule is surrounded by four B molecules and vice versa. The distances between the nearest-neighbour molecular pairs (i and ii/iii) are shown in Fig.1 [molecule i is the A molecule of (x,y, z) and (X,y, Z), ii is the B molecule of (x,y, z)and (%+ 1, y,5)and iii is the B molecule of (X+ 1/2, y,z+ 1/2) and (x-1/2, y, 5f 1/2)]. The relatively short distances (see the figure caption) between the carbon atoms of the cyano group, C(11) or C(31), and the terminal oxygen atoms of the nitroxide group, O(1) or 0(21), suggest that electrostatic energy plays a significant role in determining the molecular packing. Moreover, close spacing of the terminal oxygen atoms of the nitroxide groups and the carbon atoms of the phenyl groups, C(6) or C(26), also occurs. The dotted lines in Fig. 2 represent these short contacts. The positional interre- lation between i and ii is very similar to that between i and iii.Thus, from the magnetic point of view, a quasi-square lattice is expected to be formed in the crystal. Static Magnetic Measurements The magnetization curves at 1.8, 2.8 and 4.0 K are shown in Fig. 4. The saturation rate becomes faster as the temperature is decreased. The product of the paramagnetic susceptibility and the temperature, xpT,which is proportional to the square of the effective moment, is plotted against T in Fig. 5. Down to the lowest temperature examined (1.8 K), xpTcontinues to increase. These results demonstrate the existence of ferromag- netic intermolecular interactions. At high temperatures, >10 K, the temperature dependence J. MATER. CHEM., 1995, VOL. 5 Fig. 1 ORTEP drawing of the p-CNPNN molecules, showing the atom-numbering scheme.For simplicity, the hydrogen atoms are not shown. The atoms in the A and B molecules are represented by solid and open ellipsoids, respectively. Each molecule has a twofold axis. Symmetry operations: i, the A molecule of (x,y,z) and (X,y,3);ii, the B molecule of (x, y,z) and (X+1, y,Z) and iii, the B molecule of (X+ 1/2, y,z+ 1/2) and (x-1/2, y,Z+ 1/2). (a)Relationship between the molecules i and ii viewed along the c axis. (b) Relationship between the molecules i and iii viewedo along the a axis. Relatively short intermolecular atomic distances/A are as follows: rl, 3.45(2); r2, 3.466(8); r3, 3.433(8); r4, 3.81(2); r5, 3.82(1); rl’, 3.49(1); r2‘,3.47( 1); r3’,3.47( 1); r4’, 3.55(2); r5’, 4.13(2).of x, can be described well by the Curie-Weiss law, xp= C/(T-@), with C=0.375 emu K mol-’ and @= 1.5 K. By virtue of the mean-field approximation, where the Hamiltonian is Z =-2JCij Si-Sj,the product of the number of nearest-neighbour spins, z, and the relevant exchange interaction, J, can be estimated from the equation, 0=2zJS(S+1)/( 3kB) (1) where S =1/2. Thus zJ/kB=3.0 K. In Fig. 6, the experimental values of C/(x,T) are plotted against zJ/(k,T) with zJ/kB= 3.0K and they are compared with theoretical ones of the ferromagnetic square-lattice (2D, z =4)13 and the ferromag- netic linear-chain (lD, z=2)14 models for Heisenberg spins. The square-lattice model gives a satisfactory fit down to ca. 4 K. Therefore, it is very likely that this crystal belongs to a ferromagnetic 2D system.The deviation of the experimental result from the square- lattice behaviour below 4 K is due probably to the fact that the molecular layers in the present crystal are not exactly a square lattice. The crystal symmetry is not tetragonal, and the intermolecular couplings within the layer are not equivalent, though they are very similar. This should slightly reduce the dimensionality of the system. The second nearest-aI Fig. 2 Crystal structure of p-CNPNN viewed along the b axis. Symmetry operations are the same as those in Fig. 1. The dotted lines indicate the interactions between the nitroxide groups and the cyano or the phenyl groups. neighbour interactions and the interlayer interactions are responsible for the deviation only when they are weakly antiferromagnetic.The ac susceptibility measurements down to 0.5 K showed no sign of a magnetic phase transition.7 EPR Measurements The principal values of the EPR g factor at 293 K are guu= 2.0073, gbb =2.0066 and g,, =2.0062. These principal values correspond to the relative arrangements of the ONCNO moieties.” The small anisotropy suggests that this compound is an almost ideal Heisenberg spin system. The angular dependences of the peak-to-peak linewidth (AH,,) are shown in Fig. 7. A W-shaped angular dependence appeared within the ab and bc planes (the c and a rotations, respectively). The largest linewidth was observed for the field direction perpendicular to the ac plane, i.e.Hllb. The linewidth within the ab and bc planes went through a minimum at around 8= 55”, where 8 is the angle between the b axis and the direction of the magnetic field. This observed angular dependence is characteristic of 2D magnetic systems.16 We analysed the angular dependence of AH,, within the ab and bc plane in terms of the expression AH,, =A +B(3 COS~8-1)2 (2) Satisfactory fits to this expression were obtained, when we used A =3.3 and B =0.85 Oe for the ab plane and A =3.5 and B=0.85 Oe for the bc plane. The fits are depicted by the solid curves in Fig. 7(a)and (b). There is small angular dependence of AH,, within the ac plane. The solid curve in Fig. 7(c) represents the fit to the following equation, with A’=3.5 and B’ =0.5 Oe: AH,, =A’ +B’(1+COS~8’) (3) where 8’ is the angle between the applied field and the c axis.In an ideal 2D system, a non-Lorentzian lineshape is expected when AHppis not minimum.16 For examination of the lineshape, it may be useful to plot the quantity ~cl~’~~~l/l~’~~~ll~-~ol/~~~pp/~~11’2against CIH-HoI/ ~ ~~ 7 We acknowledge Dr. Y. Nakazawa and Professor M. Ishikawa for the ac susceptibility measurements. J. MATER. CHEM., 1995, VOL. 5 a- 4 .ML$Q-. . . . . ..., . . . . .. . . .. . . .. . . . . ... .... . . . . . .. . .. . ................................ 1 - ~1.... . ....... . . . . ..... .. . .. . . .. . . . . . . . . . . . ... . . . . . . 1 0 Fig. 3 Crystal structure of p-CNPNN viewed along the c axis 0 10 20 30 HT-'IkOe K-' Fig.4 Magnetization curves of p-CNPNN. Solid curves are theoreti- cal ones based on the Brillouin function. 0,1.8 K; 0,2.8 K; A,4.0K. t 1 1 10 100 TIK Fig. 5 Temperature dependence of xpT for p-CNPNN (AHpP/2)l2,where H, is the resonance field and I'(0) is the half-amplitude of the derivative line ]'(El). For a Lorentzian, this plot gives a straight line as shown in Fig. 8. The experi- mental results within the bc plane at 0=0 (Hllb)and 55" are also plotted in Fig. 8. A similar plot was also obtained for the ab plane. It is obvious that the lineshape is Lorentzian for Q=55". As the field is tilted from this direction, we can recognize deviation from Lorentzian as a slight broadening. However, the deviation is as small as 10% even at 15 half-widths for H(lb.This is not unexpected, because the deviation from Lorentzian in 2D systems is known to be less pro- TIK 50 10 5 4 3I ---..1D ferro ..-\0.4 1 0.2 Curie-Weiss ..Fig.6 The plot of C/(xpT) us. zJ/(k,T) for p-CNPNN with C= 0.375 emu K mol-' and zJ/k,=3.0 K (see text). The full and dashed curves show the theoretical results of a square lattice13 and linear chainI4 of Heisenberg spin with S= 1/2. The dotted line denoted as Curie-Weiss represents C/(xpT)=1-@IT [0=1 -zJ/(2kB) for s=1/21. nounced than that in 1D cases; nearly Lorentzian lineshapes are usually observed even in 2D system^.'^'^^ Discussion Now let us consider the correlation between the magnetic intermolecular interactions and the molecular arrangements.The susceptibility data above 4K are well explained by the ferromagnetic square-lattice Heisenberg model with J/kR= 0.75 K. This agrees well with the layered structure of the p-CNPNN crystal, in which the molecular sheets are piled along the b axis. The J value obtained is interpreted as the average of the two kinds of nearest-neighbour interactions in the 2D network. The 2D network in the p-CNPNN crystal consists of the interactions between the nitroxide group and the cyano or J. MATER. CHEM., 1995, VOL. 5 Hlla HNb H /la Hllc H /la Hllc 90 180 Bldegrees Fig. 7 Angular dependences of the EPR peak-to-peak linewidth (AHp,) of the (a) c, (b)a and (c) b rotations 300~ Fig.8 Analysis of the EPR derivative lineshape of p-CNPNN within the bc plane. f3 is the angle between the b axis and the direction of the magnetic field. 0,8=0" (Hllb);A,Q=55". phenyl groups. As we have emphasized previ~usly,~ the inter- action between the nitroxide (NO) group and the phenyl group (NO-.-Ar interaction) is capable of ferromagnetic coup- ling. The present compound also belongs to the category of ferromagnetic compounds which have an NO. -Ar interaction. + Next, let us direct our attention to another type of interaction, the interaction between the NO groups and the cyano (CN) groups. Note that each NO--.Ar interaction is accompanied by an NO.--CN interaction. As shown in Fig. 1, the NO and CN groups of molecule i interact with the phenyl and NO groups of molecule ii, respectively.At the same time, a similar relationship is observed between the NO and the CN groups of molecule iii and the phenyl and the NO groups of molecule i. Each molecule interacts with its four neighbours in this way. The interactions between the NO group and the para substituent have been reported for some other compounds which exhibit ferromagnetic intermolecular interactions. In the crystals of fl-,18,19y2O and 6-p-NPNN,21 the interactions between the NO group and the nitro (NO,) group are commonly formed as well as the NO.-.Ar interaction. The ferromagnetic intermolecular interaction in the p-hydroxy- phenyl nitronyl nitroxide has been interpreted also as the interaction between the NO group and the hydroxy group.22 Therefore, it seems natural to regard the NO..-CN interaction as the origin of the ferromagnetic coupling in p-CNPNN. In the present case, however, we can barely distinguish the roles of the two types of interaction in the magnetic coupling.On the other hand, the role of the CN groups as a structure- controlling factor seems to be clear when we consider the electrostatic energy between the charge distributions on the neighbouring molecules. The close spacing between the carbon atoms of the CN groups and the terminal oxygen atoms of the NO groups are naturally interpreted as a result of the positive and negative partial charges on the carbon and oxygen atoms, respectively. In this sense, the role of the CN groups is analogous to that of the NO,? groups in p-NPNN crystals.Note again that the NO...CN interactions simul- taneously afford the NO...Ar interactions. It is also suggested that the arrangement of the ONCNO groups within each sublattice of the A and B molecules is under the control of the electrostatic interactions between the ONCNO groups. As demonstrated by Awaga et ~l.,,~electro-static intermolecular interactions are useful in designing mol- ecular packing suitable for the ferromagnetic interactions. We believe that the molecular packing in the p-CNPNN crystal also illustrates the efficiency of such a strategy. Conclusion A crystal of p-CNPNN has been revealed to have a typical layered structure, in which quasi-square lattice packing occurs. Close spacing is found between the NO groups and the phenyl groups or the CN groups.From the temperature dependence of the magnetic susceptibility, the system has been charac- terized as a 2D Heisenberg ferromagnet. The analysis based on the square lattice yields the average exchange coupling, J/kB=0.75 K. This again supports our proposal that the NO-. .Ar interactions favour ferromagnetic coupling. The role of the CN groups is interpreted in terms of intermolecular electrostatic interactions. This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Area 'Molecular Magnetism' (Area No. 228/04242103) from the Ministry of Education, Science and Culture, Japan. Support from the New Energy and Industrial Technology Development Organization (NEDO) is also acknowledged.References 1 See Proc. Symp. on the Chemistry and Physics of Molecular Based Magnetic Materials, Mol. Cryst. Liq. Cryst., 1993,232 and 233. J. MATER. CHEM., 1995, VOL. 5 2 3 4 5 6 7 8 9 10 11 12 13 14 R. Chiarelli, M. A. Novak, A. Rassat and J. L. Tholence, Nature (London), 1993,363,147. T. Nogami, K. Tomioka, T. Ishida, H. Yoshikawa, M. Yasui, F. Iwasaki, H. Iwamura, N. Takeda and M. Ishikawa, Chem. Lett., 1994, 29. T. Ishida, H. Tsuboi, T. Nogami, H. Yoshikawa, M. Yasui, F. Iwasaki, H. Iwamura, N. Takeda and M. Ishikawa, Chem. Lett., 1994,919. Y. Nakazawa, M. Tamura, N. Shirakawa, D. Shiomi, M.Takahashi, M. Kinoshita and M. Ishikawa, Phys. Rev. B, 1992, 46,8906. M. Tamura, Y. Nakazawa, D. Shiomi, K. Nozawa, Y. Hosokoshi, M. Ishikawa, M. Takahashi and M. Kinoshita, Chem. Phys. Lett., 1991,186,401. Y. Hosokoshi, M. Tamura, M. Kinoshita, H. Sawa, R. Kato, Y. Fujiwara and Y. Ueda, J. Muter. Chem., 1994,4,1219. E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. Darcy, J. Am. Chem. Soc., 1972,94,7049. 0. Shimomura, K. Abe and M. Hirota, J. Chem. Soc., Perkin Trans. 2,1988, 795. C. Katayama, Acta. Crystallogr., Sect. A, 1986,42, 19. K. Awaga and Y. Maruyama, 3. Chem. Phys., 1989,91,2743. C. K. Johnson, ‘ORTEPII’; Report ORNL-5138; Oak Ridge National Laboratory: Oak Ridge, TN, 1976, vol. 22, p. 833. G. A. Baker Jr., H. E.Gilbert, J. Eve and G. S. Rushbrooke, Phys. Lett. A, 1967,25,207. M. Takahashi, P. Turek, Y. Nakazawa, M. Tamura, K. Nozawa, D. Shiomi, M. Ishikawa and M. Kinoshita, Phys. Rev. Lett., 1991, 67,746. 15 M. Kinoshita, in Magnetic Molecular Materials, ed. D. Gatteshi, 0. Kahn, J. S. Miller and F. Palacio, Kluwer, Dordrecht, 1991, p. 87. 16 P. M. Richards, in Local Properties at Phase Transitions, Proc. Int. School of Physics ‘Enrico Fermi ’, North-Holland, Amsterdam, 1976,p. 539. 17 R. D. Willett, in Magneto-structural Correlations in Exchange Coupled Systems, ed. R. D. Willett, D. Gatteschi and 0. Kahn, D. Reidel, Dordrecht, 1985, p. 269. 18 M. Kinoshita, Mol. Cryst. Liq. Cryst., 1993,22, 1. 19 K. Awaga, T. Inabe, U. Nagashima and Y. Maruyama, J. Chem. SOC.,Chem. Commun., 1989,1617; 1990,520. 20 P. Turek, K. Nozawa, D. Shiomi, K. Awaga, T. Inabe, Y. Maruyama and M. Kinoshita, Chem. Phys. Lett., 1991, 180, 327. 21 M. Tamura, D. Shiomi, Y. Hosokoshi, N. Iwasawa, K. Nozawa, M. Kinoshita, H. Sawa and R. Kato, Mol. Cryst. Liq. Cryst., 1993, 232,45. 22 E. Hernandez, M. Mas, E. Molins, C. Rovira and J. Veciana, Angew. Chem., Znt. Ed. Engl., 1993,32,882. 23 K. Awaga, T. Inabe, Y. Maruyama, T. Nakamura and M. Matsumoto, Chem. Phys. Lett., 1992,195,21. Paper 4103322A; Received 6th June, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500041

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995, 5( l), 47-52 Reproducible MOCVD of Barium Fluoride: Studies of the Effect of the Degree of Precursor Crystallinity and Purity Michael L. Hitchman"", Sarkis H. Shamlian," Douglas D. Gilliland," David J. Cole-Hamilton: Jason A. P. Nash,b Simon C. Thompsonb and Stephen L. Cook" a Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, UK G7 1XL Department of Chemistry, Purdie Building, University of St. Andrews, St. Andrews, Fife, UK KY76 9ST The Associated Octel Co. Ltd., PO Box 7 7, Oil Sites Road, Ellesmere Port, South Wirral, UK L65 4HF The previously reported varying CVD deposition rates obtained when using the new precursor [Ba(TDFND)J have been investigated using a range of techniques for analysing hydrated and anhydrous forms of the precursor before and after use for deposition.It is shown that, apart from water loss from the hydrate, there are no significant molecular structural changes to the precursor in use. X-Ray powder diffractograms do show, though, that there is the possibility of crystalline growth, and the implications of this are discussed. A simple model of spherical crystallites coalescing is considered, and it is shown that the range of behaviour observed in practice with solid precursors can be satisfactorily explained by the model. When full cognisance is taken of the effects of precursor purity and degree of crystallinity it is found to be possible to grow reproducibly high-quality BaF, and superconducting YBCO.The precursor [Ba(TDFND)J is thus a potentially useful new material for MOCVD of YBCO and other barium-containing films. For the deposition of barium fluoride and other barium- containing thin films (e.g.YBCO, BaTiO,) by CVD the most commonly used precursors are hydrates of P-diketonates with R =R'= CF, (HFAC =1,1,1,5,5,5-hexafluoropentane-2,4-dione) or R =But and R' =C3F7 (HFOD =1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione). I"However, these compounds are oligomeric, as indicated in the structural formula, and of low volatility with decomposition occurring at or close to their sublimation temperature^.'-^ This means that the reproducibility of the partial pressure of the barium precursor in the gas phase is poor and conse- quently growth rates are very variable, even if fresh samples are used for each growth run.Several approaches have been proposed to overcome this pr~blem,~ but one which we have reported on earlier is based on an analysis of published' thermal analytical data for barium P-diketonates which indi- cates that the per cent by weight left behind after sublimation (which can be regarded as a measure of the stability of a compound during sublimation) decreases in the series R' = CF, >C2F5 >C3F7with R =But in each case. This suggested that C3F7 may play a special role in reducing the degree of oligomerisation of the Ba precursor or in reducing the strength of intermonomer interactions within an oligomer. However, even for R=But, R'=C,F, (HFOD), 100% weight loss is not observed in thermal analysis, indicating that some decompo- sition occurs during sublimation.Therefore, we have investi- gated3*4 the effect of increasing the fluorine-containing substituents on the ring even further to the extent of all four groups being C3F7; i.e. [Ba(TDFND),] (where TDFND = 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluorononane-4,6-dione).In spite of a formula weight increase of nearly three times over that of an unfluorinated precursor such as [Ba(TMHD),] (where R =R' =But and where TMHD =2,2,6,6-tetramethyl-heptane-3,5-dione), the STA of the monohydrate of this com- pound [Ba(TDFND),-H,O] showed it to be more volatile than [Ba(TMHD),] and to sublime completely, after loss of water, without decomposition at 1 atm pressure.This was the first barium complex to show stable and complete volatilis- ation at ambient pressure. The high stability and volatility observed for [Ba(TDFND), -H,0] suggest that any inter- monomer forces which hold together the oligomeric structure are much lower than for other barium complexes and should make it a good precursor for CVD of barium-containing films. However, when used at 160°C for the CVD of BaF, it was found that4 whilst there was a high initial deposition rate (e.g. ca. 13.5 nm min-l) there was a sequential and marked drop in the rate when the same precursor material was used for a series of depositions (e.g.after four runs the rate was ca. 5 nm min-I). Apart from a slight discoloration of the precur- sor sample during use there was no evidence of significant decomposition of the precursor, and this was supported by the 'H and 19FNMR spectra of the used precursor being identical to those of fresh [Ba( TDFND),].Interestingly, though, we found an increase in the mp of the precursor from 187°C before use to 196°C after use. This change in the melting characteristics of the precursor on dehydration and prolonged heating, which appeared to be related to the decreases in the sublimation rate of the compound and the growth rate of BaF,, we have attributed4 to slow structural changes in the solid. In this paper we present results which show that the most significant factor giving rise to variations with usage time and sample batch of precursor volatility, and in turn CVD growth rates, can be related to differences in crystalline structure of the precursors.However, given the right conditions, stable growth rates over a number of runs can be obtained using the same batch of precursor. Experimental Full details of the synthesis of the hydrated and anhydrous forms of [Ba(TDFND),] as well as their characterisation by microanalysis and spectroscopic analysis have been given previou~ly.~.~.~For this study additional analyses were made of samples of the precursors before and after use for CVD. Microanalyses were carried out by the University of St. Andrews Materials Analysis Service. Solid-state NMR spectra were obtained with a Bruker Associates MSL 500 spec-trometer with magic angle spinning. Assignments were made using both cross polarisation (to identify C atoms directly attached to H) and high-power decoupling.Infrared spectra were obtained with a Perkin-Elmer FT 1710 Fourier-trans- form spectrometer using Nujol mulls and KBr plates. Powder X-ray diffractograms were obtained from powdered samples in sealed capillaries with a Stoe STADI P X-ray diffractometer. Thermal analyses were carried out with a Stanton Redcroft thermal analyser at atmospheric pressure under a nitrogen flow of 40 sccmt and generally at a heating rate of 20°C min-', although for detailed interpretation of TG a slower heating rate was used. A sample weight of 8 & 1mg was used. The CVD reactor system as well as the precursor subli- mation arrangement and the vapour transport handling lines have been described previo~sly.~~~ For the studies reported in this paper a precursor sublimator temperature of 160 "C was used for the Ba precursors.A substrate deposition temperature of 660°C was generally used with a total reactor pressure of 10Torr (ca. 1320 Pa), an argon precursor carrier gas flow of 200 sccm and an oxygen flow of 400 sccm. Most of the results reported are for the deposition of BaF,, but to test the precursor suitability for YBCO deposition the Y and Cu precursors which were used were [Y(TMHD),] and [Cu(TMHD),] and the precursor containers were kept at 108 and 101 "C, respectively. An argon gas flow of 200 sccm was used for each precursor and mixed oxide deposition was carried out at 750°C.Substrates for BaF, deposition were usually Si(100), but for the preparation of YBCO single- crystal MgO tiles were used. X-Ray diffractograms of deposited layers were obtained using a powder diffractometer with Cu-Ka radiation. Film thickness were determined, after photolithographic patterning and etching with a mineral acid, with a surface profilometer (Sloan Dektak 11). Thicknesses were also determined by using a two-angle ellipsometer (Gaertner L116B). The BaF, deposited with the mixed Y and Cu oxides was converted to the oxide by post-deposition annealing at atmos- pheric pressure, first in water vapour and then in O2following a recommended procedure.8 The resistance us.temperature characteristics of the annealed films were measured with a standard four-point probe over the temperature range 10-300 K. Results and Discussion We have already mentioned in the Introduction that when [Ba(TDFND), -H20] was used as a precursor for the CVD of BaF, there was a high initial deposition rate followed by a sequential and marked fall off in the rate as the precursor was used for a series of deposition^.^ This effect is shown in a different way in Fig. 1, where growth rate is plotted in the form of a histogram as a function of experimental time elapsed. We have previously attributed4 the observed decrease in growth rate of BaF, from the hydrated Ba complex to changes in the solid on heating which lead to a resulting decrease in volatility and growth rate with use.This concept is given some credence by the comparison shown in Fig. 1 between the variation of growth rate with time from the original monohydrate and from the same sample rehydrated, by boiling with water, after five runs. There is a striking similarity in the fall in growth rate with usage time for both samples. We shall mention this effect again later in the discussion, but here we note that additional support for the effect of loss of water was given by a series of 19 runs done under identical conditions over a period of 2 months from the same sample t Standard cm3 min-'. J. MATER. CHEM., 1995, VOL. 5 8/ 100 200 300 400 500 time elapsedmin Fig. 1 Growth rate of BaF, from [Ba(TDFND),*H,O] (m) and rehydrated [Ba(TDFND),] (Ed) as a function of lapsed time of anhydrous [Ba( TDFND),].These gave very constant and stable deposition rates with an average of 2.95 f0.09 nm min-l, where the error given is at the 95% confidence level for 19 runs. Further evidence that the variation of growth rate with time is related to solid structural or morphological changes rather than any inherent instability of the Ba complex is provided by several analytical techniques. First, the microanal- ysis data for a number of fresh and used samples of TDFND complexes all have the expected C and H contents (Table 1). The equivalence of solid-state NMR spectra for both [Ba( TDFND)2 H20] and [Ba( TDFND),] has already been mentioned in the Introduction, and these are shown in Fig.2. These again indicate that there is no major molecular struc- tural difference between the two samples. It is interesting to note, though, that the NMR spectra do show two distinct resonances for the carbonyl carbon atoms at 179 and 173 ppm. This indicates that either very similar molecules sit in distinctly different sites in the crystal or, more likely, that there are two different kinds of carbonyl. In the X-ray crystal structureg of [Ba(HFAC), -H20] the carbonyl groups are inequivalent as one occupies a bridging position between two barium atoms and a C-F-Ba interaction is present for one of the CF, groups on each P-diketonate (Fig. 3). The inequivalence of the carbonyl groups in [Ba(TDFND),] probably indicates bridging too, but may also arise from a C-F-Ba interaction, although it is not possible to identify which of the fluorine atoms in the C3F, groups might be involved.Support for the conclusion that there are few, if any, major molecular structural differences between the various samples was given by the IR spectra of the precursors. The FTIR Table 1 Microanalytical data for hydrated and anhydrous samples of [Ba( TDFND),] found calculated sample C(%) H(%) C(%) H(%) fresh samples: [Ba( TDFND), HzO] 22.59 0.39 22.30 0.42 [Ba(TDFND),] anhydrous 22.97 0.29 22.72 0.21 [Ba(TDFND),] dehydrated 22.93 0.23 22.72 0.21 used samples: [Ba(TDFND), .HzO] 22.62 0.21 22.72" 0.21" [Ba(TDFND),] anhydrous 22.63 0.23 22.72" 0.21" For [Ba(TDFND),].J. MATER. CHEM., 1995, VOL. 5 (a) I I I I I I 180 160 140 120 100 80 I 1 I I I I 180 160 140 120 100 80 1 I I I I I 180 160 140 120 100 80 s Fig. 2 Solid-state NMR spectra for (a)dehydrated (b)hydrated, and (c) anhydrous samples of [Ba( TDFND)J Fig. 3 Schematic structure of [Ba(HFAC), -H,0] showing the non- equivalence of the carbonyl groups of each hexafluoropentanedionato ligand. One set of carbonyl groups is shown by bold oxygen atoms. R =CF, spectra for hydrated, dehydrated and anhydrous samples of [Ba(TDFND),] were all essentially identical, with the notable exception that unused [Ba( TDFND), H20] gave a broad absorption based at 3567 cm- corresponding to coordinated water.There were other minor differences with, for example, a very weak absorption at 1020cm-' for all samples except the sample of unused [Ba(TDFND), *H20] and a very weak shoulder at 625 cm-I for that sample appearing at 617 cm-I for all of the other samples. These differences were slight, though, and one can only conclude again that all of the samples had essentially identical molecular structures. Powder X-ray diffractograms of the various precursor samples did, however, show some interesting differences (Fig. 4). Although the quality of the data is not good, perhaps because the barium atom has a large absorption cross-section for X-rays, a comparison of the diffractograms does allow some general observations to be made. All of the patterns show a sharp, intense peak at 28 M 8 O and two much weaker peaks in the range 28=18-19".For fresh [Ba(TDFND),. H20] [Fig. 4(a)] there is a small, sharp peak at 28 M 7 O and two other similar peaks in the region 28= 15-16 O. For the other samples [Fig. 4(b)-(e)] these peaks are absent, but they all show instead a cluster of peaks in the range 28= 17-18 '. The only other notable differences in the powder diffraction data are the presence of a peak at 28 M 5.5 O for dehydrated [Ba( TDFND), H20] [Fig. 4(e)] and a peak at 28 M21.2 O for the used hydrated precursor [Fig. 4(b)]. All of the samples show a very broad, low-intensity diffraction band from 28~14-40 O. This broad absorption is more apparent for [Ba(TDFND), *H20] [Fig.4(a)] and the sample obtained by I I* 10 20 30 40 2Bldegrees Fig. 4 X-Ray powder diffractograms for various precursor samples: (a) unused hydrated precursor [Ba(TDFND), -H,O], (b) hydrated precursor [Ba(TDFND), .H,0] after four growth runs, (c) unused anhydrous precursor [Ba( TDFND),] , (d) anhydrous precursor [Ba(TDFND),] after four growth runs, (e) hydrated precursor [Ba(TDFND), H,O] after heating in uucuo at 106 "Cfor 2.5 days dehydrating this compound [Fig. 4(e)] than for the other samples. It may suggest the presence of an amorphous phase. The powder X-ray diffraction data again show that the basic molecular structure of all the samples is similar, with differences arising primarily for the hydrate and its dehydrated forms.What is probably more significant, though, is that there is a tendency for the peaks in the diffraction patterns of samples which have been used to be sharper; this is particularly noticeable in the case of anhydrous [Ba(TDFND),] after four growth runs [Fig. 4(d)]. Generally, very small crystallites give broad diffraction patterns whilst larger crystals give sharper peaks. Heating samples close to their melting points may well lead to annealing and resultant crystal growth and an increase in crystal size. Thus anhydrous [Ba(TDFND),], with an mp of 196 "C, held at 160°C for at least 4 h shows good evidence of crystal growth [Fig. 4(d)], while the initially hydrated sample which is dehydrated at 106" under vacuum for 2.5 days shows the next sharpest peaks [Fig.4(e)].In contrast, unused, anhydrous [Ba(TDFND),] [Fig. 4(c)] gives broader peaks than any other sample. Since we have no evidence for significant differences in molecular structure between sample batches or for structural changes with sample usage it seems likely that changes in crystallinity are related to changes in growth rate with time. Let us now consider what the effect of annealing and crystal size increase might be. It can be readily shown that, if one assumes spherical crystallites, the overall surface area will decrease by a factor of n-'I3, where n is the number of small crystallites being incorporated into a larger single crystallite. We have shown" that with the design of precursor container which we used, and which is a commonly used design, the rate of evaporation of precursor is mainly under mass-trans- port control.Therefore, the pick-up rate by the carrier gas and, hence, the precursor partial pressure and the CVD growth rate will also fall by a factor of for example, the coalescence of just two crystallites will lead to an effective growth rate decrease of ca. 20% for precursor vapour originat- ing from the single crystallite. With this simple model one can begin to understand a range of variable results obtained previously. First, the decrease in growth rate with time already mentioned (cJ: Fig. 1) of ca. 40% for a hydrated sampled of [Ba(TDFND),] arises not only because of dehydration, but also because of annealing and crystal growth.We have also observed a fall in growth rate with time for an anhydrous sample of [Ba( TDFND),] for which the initial value was 3.1 nm min -' and for which a value of 2.5 nm min-' was obtained after four growth runs. The decrease in this case was only ca. 19%, which is less than that found with the hydrated sample, and this is not too surprising since one might expect there to be rather more crystal reorganisation on the dehydration of an initially hydrated sample; the overall changes in the X-ray diffractograms in going from unused hydrated precursor [Fig. 4(a)] to used precursor [Fig. 4(b)] are more dramatic than in going from unused anhydrous precursor [Fig. 4(c)] to used precursor [Fig. 4(d)]. We have, though, obtained as mentioned earlier, very reproducible growth rates with anhy- drous precursor: 2.95f0.09 nm min-'.With yet another anhydrous sample we have also obtained self-consistent results, but at a considerably lower rate: 2.11 fO.04 nm min-' for six runs. These stable growth rates may seem, at first sight, to be contrary to our thesis of the effect of changes in crystal size. However, from the time that we started to use solid precursors for CVD of high-temperature superconductors we have seen this very varied behaviour in deposition rates both with time and for different samples of precursor, and we have always suspected that it was, at least in some way, related to differences in solid division of the samples. To try to offset J. MATER. CHEM., 1995, VOL.5 this effect we have usually compressed the solid precursor material into a flat pellet. This has been done by having a short cylindrical tube, sealed at one end and holding 1-2 g of precursor. The precursor has then been compressed into a pellet in the base of the tube by using a plunger and a hydraulic press operated at a pressure of about 3000 kg cmP2. The resulting 3-4mm deep pellet in the tube has been found to give a more reproducible, although lower, growth rate than when just loose precursor was used. These observations are again consistent with the simple model of surface area affecting vaporisation rates and, in turn, growth rates since a com-pressed pellet is likely to have a lower area and to retain a more consistent area than loose material.There have, though, as we have indicated still been variations in growth rate between batches and these probably have resulted from initial differences in crystalline form which have led to different degrees of compressibility of the precursor material. This effect of initial degree of crystallinity can be illustrated by deliber- ately varying it before compression of the precursor. For a sample of very carefully purified and crystallised [Ba(TDFND),] precursor reproducible growth rates can be obtained [Fig. 5(a)]. A sample of the same precursor which was slightly 'wet' due to retention of unreacted ligand HTDFND showed a high initial deposition rate and then a gradual decrease with usage [Fig. 5(b)]. This is understandable in terms of solvent loss resulting in possible fractures being introduced into the precursor pellet and accompanied by the annealing effects mentioned above. Taking the pure sample (a) and deliberately contaminating it with HTDFND gives results [Fig.5(c)] remarkably similar to those of the sample which was initially impure. Further evidence of the effect of differences in crystal size can be seen from TG plots. These are often used to compare the relative volatilities of samples. Fig. 6 shows high-resolution TG traces for hydrated used and anhydrous used samples. The used hydrated material starts to lose weight at a lower temperature and more rapidly than the used anhydrous sample. The additional weight loss for the used hydrated sample cannot be due to simple loss of water of crystallisation since this will have been driven off during usage as a CVD precursor.Let us consider the evaporation of precursor from the surface of spherical crystallites. If it is assumed that the radial diffusion is governed by a surface condition -D acpr =U(C,-c,) (1) where D is the diffusion coefficient for the precursor in the 8/ 0 A 0 A 0 100 200 300 400 time elapsedmin Fig. 5 Growth rate of BaF, from samples of [Ba(TDFND),] of varying purity as a function of lapsed time: M,dry; A, slightly wet due to retention of HTDFND; 0, as for H but with 10% HTDFND added J. MATER. CHEM., 1995, VOL. 5 150 200 250 T/"C Fig.6 TG plots of (a) used hydrated and (b)anhydrous samples of [Ba(TDFND),] solid, aC/& is the radial concentration gradient, a is the ratio of volumes of the surrounding atmosphere and the spherical crystallite, and Cs and Co are, respectively, the concentrations just within the sphere and outside the sphere, then the total amount of diffusing substance leaving the sphere at any time (t)is given by'' In this equation MJM, is the mass ratio with respect to the steady state, LFaa/D, a is the radius of the sphere, and p,, are the roots of Pnc0tPn+ L -1=o (3) Fig.7 shows the curve for L= 1 for the ratio MJM, as a function of (Dt/a2)'I2.The first thing to note from this figure is that the amount of precursor evaporating at any given time is inversely proportional to the radius of the sphere.For the TG traces shown in Fig. 6 the temperature scale is equivalent to a timescale since the same temperature programme was applied to both samples. Therefore at a given temperature a greater weight loss will be indicative of a smaller sphere radius. This is seen to occur for the used hydrated sample. On comparing the growth rates obtained with the two samples it was found that the used hydrated material gave a larger value (ca. 5 nm min-') than the used anhydrous material (ca. 3 nm min-I), which, on the basis of the argument given earlier, means that the former sample consists of smaller crystallites than the latter sample. Thus the results from the growth studies and the TG plots are consistent. Furthermore, the smaller the sphere radius the steeper is the slope aM,/at in Fig.7 and the greater the expected weight loss per unit 0.0 0.0 0.5 1.0 1.5 2.0 (Dfla?-)"* Fig. 7 Plot of eqn. (2) for L= 1 time for a TG, at least for the major part of the curve. This is also seen to be the case in Fig. 6. Finally, as M,+M, the slope aM,/at in Fig. 7 becomes independent of the radius a and again this is apparent in the TGs when most of the samples have been evaporated. Thus, overall, the model of the effect of crystal size on evaporation rate and growth rate is seen to explain satisfactorily the range of behaviour observed in practice. Of course, an excess amount of a ligand such as HTDFND added to the precursor solid could be considered to act as a Lewis base, hindering intermolecular bonding between mol- ecules and the formation of low-volatility oligomers.This would manifest itself in a similar effect on growth rate with sample usage to that observed for crystalline growth; i.e. a gradual decrease in growth rate as with continuous usage and heating of the precursor the excess of ligand is driven off. This type of behaviour, which could be expected to be especially applicable to Ba precursors because of the tendency of the element to increase its coordination number,', would mean that a fresh sample of anhydrous material which is slightly contaminated with any Lewis-base impurity would then show a high initial growth rate because of enhanced volatility, but as the impurity is slowly lost there would be a fall off with time in the transport rate of the precursor to the reactor, leading to a concomitant decrease in growth rate.This effect could be accentuated by annealing and crystallisation changes with time. If a Lewis-base adduct is being formed from an impurity it is analogous to the enhanced volatility which has been observed for, for example, with [Ba(TMHD),] (R =R' =But) when NH3,13 or tetrahydr~furan,'~ or HTMHD" is intro- duced into the carrier gas. However, the DTA plots for carefully purified anhydrous [Ba( TDFND),] and anhydrous [Ba( TDFND),] contaminated with HTDFND showed, apart from the loss of the excess HTDFND at ca. 70°C for the contaminated sample, identical features including, most notably, identical mps.Therefore if the chemical effect is playing a role in the observed variation of growth rate it may be because it is more difficult to remove the excess of ligand from a highly compressed pellet than from a loose sample such as is used in a DTA experiment; this may also be true in the case of loss of water from the hydrate, discussed earlier (cf: Fig. 1). The overall evidence suggests, though, that the effect of formation of a Lewis base is a secondary one with the physical effect of recrystallisation being the main factor causing variable growth rates. For MOCVD of high-temperature superconductors and related materials the implications of these findings are that it is essential to control not just the purity of a precursor but also its crystal form.By attempting to do this using carefully purified [Ba(TDFND),] compressed into a pellet we have been able to obtain reproducible growth from this new precursor and our earlier concl~sion~*~ that it might prove difficult to use it in the MOCVD of, for example, high-quality BaF, films and superconducting layers of YBCO, where reproducible control of stoichiometry is an essential prere- quisite, was overly pessimistic. In fact, we have prepared epitaxially oriented ( 111) BaF, films and superconducting YBCO films, under the conditions described above, using anhydrous [Ba( TDFND),]. For the YBCO layers semicond- ucting resistivity is seen at high temperatures and the onset of superconductivity is at ca. 82 K with zero resistance being attained at 75.3 K.These values could undoubtedly be improved upon by optimising the deposition and annealing conditionq8 and this is currently being investigated further. Conclusions The potential value of [Ba(TDFND),] as a volatile and stable precursor for deposition of BaF, and, by hydrolysis, of BaO in YBCO is apparent. The importance of careful attention to precursor purity and, especially, crystalline form is equally apparent, though, and this conclusion is probably generally applicable to the other organometallic precursors used for MOCVD of YBC0l6 and other 1a~ers.l~ In particular, the influence of gradual annealing of solid precursor samples resulting in crystalline growth, reduction in surface area and decreased pick-up rates by the carrier gas highlights the value of having a precursor which is a liquid at the temperature of sublimation.We have recently reported6 on just such a precursor for BaF, deposition which extends the use of [Ba(TDFND),] by enhancing its volatility through the syn- thesis of an adduct with tetraglyme. This [Ba(TDFND),. tetraglyme] complex has an mp of 70°C and is the most volatile and stable barium precursor under atmospheric con- ditions yet reported. Of course, for YBCO preparation, use of either pure, anhydrous [Ba(TDFND),] or the tetra-glyme complex requires in situ or post-deposition hydrolysis of the fluoride which is deposited rather than the oxide. Although this is not necessarily a disadvantage from the point of view of layer properties, it could be a drawback from the point of view of operation of a gas-handling system since it requires an additional control line.No non-fluorine-contain- ing barium precursors, including the recently reported new alkoxides," show the same degree of stability, volatility and reproducibility that we have found for the TDFND complexes, including anhydrous [Ba( TDFND),] reported on here. We gratefully acknowledge the support of the Commission of the European Communities under the BRITE/EURAM Programme, Contract No. BREU 0438, and of The Associated Octel Co. Ltd for three studentships (D.D.G., J.A.P.N. and S.C.T.) and other financial assistance. We thank Mr. R. P. McGinty and his colleagues for carrying out the thermal analyses, Dr.J. Nowiski for producing the powder diffracto- grams and Drs. F. G. Riddell and P. G. Bruce for helpful discussions. J. MATER. CHEM., 1995, VOL. 5 References 1 A. P. Purdy, A. D. Berry, R. T. Holm, M. Fatemi and D. K. Gaskill, Inorg. Chem., 1989,28,2799. 2 C. O-Gonzalez, H. Schachner, H. Tippmann and F. J. Trojer, Physica C, 1988,153-155,1042. 3 S. C. Thompson, D. J. Cole-Hamilton, D. D. Gilliland and M. L. Hitchman, Adu. Muter. Opt. Electron., 1992, 1, 81. 4 D. D. Gilliland, M. L. Hitchman, S. C. Thompson and D. J. Cole-Hamilton, J. Phys. (Paris) 111, 1992, 2, 1381. 5 R. Belcher, C. R. Cranley, J. R. Majer, W. I. Stephen and P. E. Uden, Anal. Chim. Acta, 1972,60, 109. 6 S. H. Shamlian, M.L. Hitchman, S. L. Cook and B. C. Richards, J. Muter. Chem., 1994, 4, 81. 7 S. C. Thompson, D. J. Cole-Hamilton, S. L. Cook and D. Barr, Eur. Pat. Appl., 1993,92307390. 8 P. S. Kirlin, R. Binder, R. Gardiner and D. W. Brown, SPIE Processing of Films for High Superconducting Electronics, 1989, 1187,115. 9 D. C. Bradley, M. Hasan, M. B. Hursthouse, M. Montevalli, 0.F. Z. Khan, R. G. Pritchard and J. 0.Williams, J. Chem. SOC., Chem. Commun., 1992,575. 10 M. L. Hitchman and D. D. Gilliland, in Proc. 8th CIMTEC World Ceramics Congress and Forum on New Materials, ed. P. Vincenzini, Techna, Faenza, in the press. 11 J. Crank, The Mathematics of Diflusion, Clarendon Press, Oxford, 2nd edn., 1975, ch.6. 12 M. L. Hitchman, D. D. Gilliland, D. J. Cole-Hamilton and S. C. Thompson, Inst. Phys. Conf. Ser., 1990, 111,305. 13 A. Barron, Strem. Chem., 1990,13, 1. 14 S. Matsumo, F. Uchikawa and Y. Yoshizaki, Jpn. J. Appl. Phys., 1990,29, L947. 15 F. Schmaderer, R. Huber, H. Oetzmann and G. Wahl, J. Phys. (Paris) III, 1991, C2, 539. 16 M. L. Hitchman, S. H. Shamlian, D. D. Gilliland, D. J. Cole-Hamilton, S. C. Thompson, S. L. Cook and B. C. Richards, in Proc. Symp. MOCVD Electronic Ceramics, ed. S. B. Desu, D. B. Beach, B. W. Wessels and S. Gokoglu, MRS, Pittsburgh, 1994, p. 249. 17 B. R. Butler and J. P. Stagg, J. Crystal Growth, 1989,94,481. 18 W. A. Herrmann, N. W. Huber and T. Priermeier, Angew. Chem., Int. Ed. Engl., 1994,33, 105. Paper 4/03992K; Received 1st July, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500047

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995, 5( l), 53-56 Electrical Conduction of Yttrium-doped Strontium Zirconate Peng-nian Huang and Anthony Petric* Department of Materials Science and Engineering, Mc Master University, Hamilton, Ontario, Canada L8S 4L 7 Solid solutions of SrZr, -,Y,O, -o,5x having orthorhombic perovskite-type structure with 0 <x <0.2 have been studied. The conductivity increased and the activation energy decreased with yttrium content up to x=O.2 at low temperature or x =0.05 at high temperature. The proton and oxygen transference numbers measured in H20and oxygen concentration cells, respectively, indicated that this material is a good oxygen ion conductor from 400 to 600 "C. At lower temperatures the material was predominantly proton conducting and at high temperatures, the hole conductivity increased until it predominated above 800 "C.The substitution of Y3+ for ZP+ had no significant effect on the transference numbers. It is generally accepted that oxygen electrolytes are of key importance in sensors, oxygen pumps and especially in solid oxide fuel cells (SOFC). The most successful electrolyte ma- terials for high-temperature fuel cells are based on stabilized zirconia. These materials, however, are still not popular in commercial use because they require relatively high operating temperatures, which causes electrode reactions and other engineering problems associated with seals and electrical feedthroughs. Thus there is continuing interest in research on alternative materials for fuel-cell electrolytes.Structurally, the most extensively studied anion electrolytes have a fluorite or related structure. Unlike the fast F-ion conductors, for example, PbF, and PbSnF,, which exhibit smooth transitions to fast conduction below their melting the oxide compounds with the fluorite struc- ture have interesting oxide ion conductivity only if solid solutions are formed by addition of either an alkaline-earth- metal oxide or a rare-earth-metal oxide., The presence of the divalent or trivalent cations on the cation sublattice results in the formation of anion vacancies to preserve electrical neutrality. The oxygen ions are predominantly mobile via an oxygen vacancy mechanism., In addition to fluorite-type materials, perovskite (ABO,) materials commonly form solid solutions because the structure is very tolerant of changes in the ionic radii of the A and B Therefore, substitution of A or B ions by lower-valent cations introduces anion vacancies, resulting in oxide ion conduction.The initial studies of Takahashi and Iwahara* indicated that perovskite solid solutions exhibited high oxygen ion conduction at low oxygen pressure, but this was accompanied by p-type electronic conduction at high oxygen pressure. Later work on strontium9 and cerate-based materials showed that they were oxide ion conductors in oxygen-rich atmospheres and proton conductors in hydro- gen-rich atmospheres. Iwahara et a1.12 reported that of these materials, BaCe, -,Sm,03 offered the best performance for solid oxide fuel-cell applications amongst the various perov- skites tested. Recent reports on perovskite electrolytes have been directed at the proton conduction and catalytic behav- iour of these materials, especially in the rare-earth-metal doped cerates and zircon ate^.'^-'^ Earlier studies on the electrical conductivity of single crystal and polycrystalline Y-doped SrZrO, found proton conduc- tion,15*16as well as oxygen ion and hole conduction, at high temperat~re.'~The aim of the present work was to study systematically the solid-solution formation of Y-doped SrZrO, and to determine the electrical conductivity by ac impedance and electrochemical measurements.Experimental SrC0, (Fisher 99.5%), ZrO, (TOSOH TZ-0) and Y,O, (99.99%, Strem Chemicals Inc.) were used as starting mate- rials.The powders were mixed, pelletized and fired at 1300 "C for 24 h. Complete solid-solution formation was confirmed by X-ray diffraction using an IRDAB Guinier camera with Cu- Karadiation and silicon as an internal standard. The synthe- sized powders were reground, repelletized and sintered at 1500-1600°C for 24 h. The density of the sintered products was found to be >95% of the theoretical value. Specimen discs of 11 mm diameter and 5 mm thickness were painted with silver paste (Johnson Matthey LM-MH201B) and fired at 850°C for 15 min. The electrical conductivity measurements were carried out using a Schlumberger 1260 impedance/gain-phase analyser interfaced to a computer equipped with 260 software (Scribner Associates Inc.).The measured frequency ranged from 1 Hz to 1 MHz. The cell emf was measured using a Keithley model 6 14 electrometer. Since these materials are highly hygroscopic, the dc conductivity measurements were taken without delay, usually 1 day after sintering. Results and Discussion The X-ray diffraction pattern of the sintered SrZrO, specimen showed an orthorhombic perovskite-type structure with a = 0.5798 nm, b=0.8203 nm and c=0.5818 nm, in good agree- ment with the results of Swanson et d.,*For the yttria-doped compositions, SrZr, -,Y,03 -0.5,, a single-phase solid solution was formed between x=O and 0.2. The oxide ion or proton transference numbers in solids can be obtained from measurements of the open-circuit voltage of corresponding gas concentration cells and the Nernst equa- tion. For the oxide ion transference number, to, the Nernst equation has the form: Kp =to(RT/4F1In (P"o,Po,) (1) where Po, is the oxygen pressure on either side of the electrolytes.For the proton transference number, tH, the Nernst equation is written as: ~~(P"H,/PH,) (2)Kp = -~H(RT/~F) In practice, the gas pressure is fixed by the pure gas or a gas mixture on the two sides of the concentration cell.'' From the equilibrium 2H20k2H2 +02,eqn. (2) becomes '/op = -tH (RT/2F )In IPH~0) (3) For mixed oxide-proton conductioz ?he Nernst equation takes the form: Kp=~~RT/~F)~~(P"o~/Po~)-tH(RT/2F)ln(P"HZ/PH,) or In this work, two kinds of gas concentration cells were used.In the first case, the oxygen pressure was fixed by an oxygen-argon mixture (Po2=20 kPa) on one side and pure oxygen (Po2=101kPa) on the other. Hence, eqn. (1) defines the emf. For the proton concentration cell, the gases consisted of ambient air on one side and air with 10ppm water vapour on the other. Since both sides had the same oxygen pressure, the Nernst equation can be expressed by eqn. (2). Fig. 1shows the electrical conductivity of SrZr, -xY,O, -o.5x at various values of x measured in air. Some of the peaks in the X-ray pattern of the x=0.3 sample indicated the onset of a second phase. In the temperature range indicated, the electrical conductivity of pure SrZrO, obeys the Arrhenius relation: 0=oo/Texp(-Ea/kT) (5) with a single activation energy E,.The conductivity of yttria- doped samples increased significantly with yttrium content. The Arrhenius plots of the doped samples show a change in activation energy at about 550°C. It can be assumed from the transference numbers that the change in activation energy of doped samples originated from the change in conductive species, i.e. the materials were mixed oxygen-proton conduc-tors at lower temperatures and mixed oxygen-hole conductors at higher temperatures. As shown in Fig. 2 and Table 1, the samples with the highest conductivity and lowest activation energy are x=0.2 in the low-temperature regime and x =0.05 in the high-temperature regime. The conductivities of SrZro.95Yo.0502.95are consistent with those reported by Huang and Ishigame.16 It is believed that the oxide ions in oxygen electro- lytes migrate uia oxygen vacancie~.~ In pure SrZrO,, oxygen vacancies originate from the defect structure based on the following equilibria? 0=Vsr"+VZ~"''-k 3Vo" (6) K1=[Vsr"][VZr""][VO'.]3 (7) The oxygen vacancies can combine with the oxygen in air to produce excess holes, 10 1 7 5 0 10" 0 z I-b 0 Om 0 A 8." m A 0 m 10-2 lo-: 0.8 1.2 1.6 lo3 WT Fig.1 Conductivity of SrZr1-xYx03-o.5xin air for x: 0,0; 0,0.02; 0,0.05; A,0.1; A, 0.2; .,0.3 J. MATER. CHEM., 1995, VOL. 5 r 0.0 0.1 0.2 0.3 X Fig.2 Conductivity of SrZrl~xYx03~o,5x andin air at 400°C (0) 800 "C (0) Table 1 Activation energies at low temperatures (LT) and high temperatures (HT), conductivities at 600 "C and pre-exponential factors of SrZr, -xYx03-0.5x 0 0.84 5.75 x 10-5 ~~ 5.13x 104 0.02 1.01 0.70 2.63 x 10-4 7.02 x 103 0.05 0.96 0.42 1.41x 9.21 x 10' 0.45" 0.54" 1.41 x lop3" 0.1 0.71 0.52 9.33 x 10-4 4.1 x 103 0.2 0.70 0.64 8.32 x 10-4 1.03 x 104 " Single-crystal data.8 where 0, is an oxygen ion on a normal lattice site, VSrffand VZr'"' are strontium and zirconium vacancies, respectively.When the material is exposed to an atmosphere containing water vapour, the following equilibrium is established: 2H20( g) +4h' =4Hi' +O2 (10) Combined with eqn. (8), this becomes H20 +Vo"= 2H; +0, (11) K3 =CHi'12/(PH20CVo"I) (12) Finally, the equilibrium between valence electrons (n) and electron holes (p) is given by O=e'+h' (13) K4=np (14) Based on the above equilibria, there are four possible charge carriers, i.e.oxygen vacancies, protons, holes and electrons. The charge carrier densities depend on the equilibrium con- ditions given above. Thus we can write the total conductivity, gtotal, as gtotal= go2-+gH++ +oe (15) The transference numbers, therefore, depend on the above equilibria, which are fixed by the measurement conditions, including oxygen and water vapour pressure and temperature. The proton and oxide ion transference numbers of the SrZrO, sample shown in Fig. 3 indicate that (i) at lower temperatures, the conduction is predominantly protonic, (ii) at temperatures ranging from about 400 to 6OO0C,conduction is by oxide J.MATER. CHEM., 1995, VOL. 5 lo-*[a / 0 c 300 500 700 900 T/'C Fig. 3 Transference numbers for polycrystalline SrZrO,. The hole transference number, th (A), was calculated from the measured transference number, to (0),and the proton transference number tH ions and (iii) at high temperatures, charge transport occurs increasingly by hole conduction. In this work, higher oxygen pressures were used for determining the oxygen transference numbers. If the oxygen pressure is lower, a wider temperature range for predominant oxide ion conduction can be expected. Furthermore, if the oxygen pressure is low enough, n-type electronic conduction will occur.For Y-doped SrZrO,, the ionic size difference would indi- cate that Y3+ ions prefer Zr4+ sites rather than Sr2+ sites. The Y3+ substituted for Zr4'- in SrZrO, will provide oxygen vacancies" and the reaction can be expressed as Y3+=Yzr'+ 1/2 V0" (16) where Y,, denotes Y3+ substituted for the Zr4+ sites. Initially, the conductivity increases sharply with the substitution of Y3+ for Zr4+ in SrZrO,, as shown in Fig. 1 and 2. However, such a substitution, as seen in Fig.4, does not significantly change the transference numbers in the low and middle temperature ranges and at higher temperatures, increases slightly the hole transference number. 10 lo2 lo3 lo4 lo5 frequency/Hz Fig. 5 Frequency dependence of conductivity in SrZr,,,Yo,,O, 0, 406 "C; A,805 "C Because of the relaxation effects associated with proton or oxide ion mobility, the conductivity at low temperature and low frequency was found to be frequency dependent as shown in Fig.5. At high temperature, the conductivity was indepen- dent of frequency, owing, in part, to the hole conductive character of the solid. In most earlier studies, SrZr0,-based materials were con- sidered as only proton conductors. Iwahara et found SrZro.95Yo,0502.95to be a good proton conductor in a hydro- gen atmosphere at temperatures up to 1000°C. Huang and Ishigame16 proposed that Y-doped SrZrO, single crystals had only two types of charge carrier, i.e. holes and protons. The oxygen vacancies and the electrons were totally neglected.Because of the equilibria among four types of charge carriers, i.e. oxygen vacancies, protons, holes and electrons, the conduc- tivities and especially transference numbers will largely depend on measurement conditions, namely, oxygen pressure, hydro- gen or water vapour pressure and temperature for various levels of doping. Conclusions Solid solutions of SrZr, -,Y,03-0.5, with orthorhombic per- ovskite-type structure were synthesized in the range 0<x <0.2. The conductivity increases and the activation energy decreases with yttrium doping up to x=0.2 at low temperature and x= 0.05 at high temperature. The proton and oxide ion transfer- ence numbers, measured on water vapour and oxygen concen- tration cells, respectively, indicate that at lower temperature the materials are predominantly proton conducting, at tem- peratures from 400 to 600 "C they are good oxide ion conduc- tors, and at high temperatures hole conductivity predominates. The substitution of Y3+ions for Zr4+ ions has no significant effect on the transference numbers because the oxygen vacanc- ies resulting from such a substitution promote not only oxide ion conduction but also proton conduction at low temperature and hole conduction at high temperature.In certain oxygen Oe2 pressure and temperature ranges and in the absence of hydro- t gen in the environment, Y-doped SrZrO, materials are good 0.01oxide ion conductors. High hydrogen pressure, however, will300 500 700 900 favour proton conduction. TI'C Fig.4 Oxide ion transference numbers for SrZrO, (0) and We wish to acknowledge the financial support from the srzr0.95y0.0502.975 (O) Department of Energy, Mines and Resources of Canada. 56 J. MATER. CHEM., 1995, VOL. 5 11 J. S. Liu and A. S. Nowick, Solid State lonics, 1992,50, 131. References 12 H. Iwahara, T. Yajima, T. Hibino and H. Ushida, J. Electrochem. 1 M. Faraday, Experimental Research in Electricity, Taylor and Soc., 1993, 140, 1687. Francis, 1939. 13 S. Hamakawa, T. Hibino and H. Iwahara, J. Electrochem. Soc., 2 C. Lucat, Thesis No. 604, University of Bordeaux, 1980. 1994,141, 1720. 3 T. H. Estell and S. N. Flengas, Chem. Rev., 1970,70, 339. 14 K. C. Liang and A. S. Nowick, Solid State Ionics, 1993.61,77.4 C. Wagner, Naturweiss., 1943,31, 265. 15 H. Iwahara, T. Yajima, T. Hibino, K. Ozaki and H. Suzuki, Solid 5 T. Takahashi and H. Iwahara, Denki Kagaku, 1967,35,433. State lonics, 1993,61, 65. 6 T. Takahashi, in Physics of’ Electrol-ytes,ed. J. Hladik, Academic 16 H. H. Huang and M. Ishigame, Solid State Ionics, 1991,47,251. Press, 1972, vol. 2. 17 K. W. Browall and 0.Muller, Muter. Res. Bull., 1976, 11, 1475. 7 K. W. Browall, 0.Muller and R. H. Doremus, Muter. Res. Bull., 18 H. E. Swanson, M. I. Cook and T. Isaacs, Nut!. Bur. Stund. Circ., 1976,11, 1075. 1960,539, 5 I. 8 T. Takahashi and H. Iwahara, Energy Conversion, Pergamon 19 T. Norby, Solid State Ionics, 1988,28-30, 1586. Press, 1971, vol. 11, p.105. 20 H. Uchida, N. Maeda and Iwahara, Solid State lonics, 1983, 11,9 N. Bonanos, B. Ellis and M. N. Mahmood, Solid State Ionics, 117.1988,28-30,579. 10 D. A. Stevenson, N. Jiang, R. M. Buchanan and F. E. G. Henn, Solid State Ionics, 1993,62, 279. Paper 41039636; Received 30th June, 1994

ISSN:0959-9428    

DOI:10.1039/JM9950500053

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

J. MATER. CHEM., 1995,5( l), 57-63 Citrate Route to Ultra-fine Barium Polytitanates with Microwave Dielectric Properties Jin-Ho Choy,*" Yang-Su Han,a Jin-Tai Kim" and Yoon-Ho Kim,b a Department of Chemistry, Seoul National University, Seoul, 7 57 -742, Korea Dielectric Ceramics Laboratory, Korea lnstitute of Science and Technology, Seoul, 730-650, Korea Highly reactive and ultra-fine barium polytitanates (BaO-nTiO,, n =4, 4.5, 5) with a particle size of 30-50 nm have been prepared by the citrate route. Solubility isotherms were calculated for the BaC0,-citric acid-H,O and TiO(OH),-citric acid-H,O,-H,O systems at 25 "C to predict the optimum pH condition for preparing pure and stable citrate complexes. Pure and well crystallized powders with monodispersive, nanometer-sized particles could be obtained by thermal decomposition of the optimally prepared citrate precursors at relatively low temperatures.Details of the crystallization process and particle characteristics of citrate-derived barium polytitanates are described. The sinterability and micro- wave dielectric properties of BaTi,O, and Ba2Ti9020 were also measured and are discussed briefly. Dielectric materials used for dielectric resonators at micro- wave frequencies (UHF and SHF) are required to have dielectric properties as follows:',2 high relative permittivity, E, (the size of the dielectric resonator is proportional to l/~,''~), extremely low dielectric losses (high Q, Q is given by l/tan 6, tan 6 =dielectric loss) and a small temperature coefficient of resonant frequency, zf.Among the BaO-nTiO, materials with a Ti0,-rich region, the compounds with n= 4, 4.5 and 5, i.e., BaTi,O,, Ba2Ti9020 and BaTi,O,,, have attracted a lot of attention because they have superior dielectric properties for microwave resonator applications. The reported dielectric properties so far are E, = 39.8, Q =9000 at 4 GHz, .rf=2 ppm 'C-' for Ba2Ti9020 and E, =38, Q z 8000 at 4 GHz, zf= 15 ppm "C- for BaTi,O,, respe~tively.~~~The dielectric properties of BaTi,O,, , which has not been synthesized by solid-state reaction, were reported recently as ~~~440 and Q >6000 at 9.7 GHz for the sample prepared by an alkoxide sol-gel method. The experimental data, however, show a higher zf of ca. 40ppm OC-l due to the coexistence of TiO, as a decomposition product from BaTi,O, .6 For the preparation of pure crystalline Ba-polytitanate materials from BaCO, and TiO, by the conventional solid- state reaction, it is necessary to control precisely the stoichi- ometry, since there are various thermodynamically stable compounds in the vicinity of the desired composition of the Ti0,-rich BaO-TiO, system.In addition, a high sintering temperature (> 1400 "C) is indispensable to obtain dense ceramics by the conventional method. However, use of such an extremely high temperature leads to compositional and structural defects because of the evaporation of some constitu- ents, such as BaO, and the reduction of Ti4+ to Ti3+, which leads to a severe degradation of the dielectric properties.In order to overcome such problems, various chemical routes, mainly based on the hydrolytic precipitation of alkox- ides, have been developed6-' and are still under investigation. The liquid-mix process (the so called Pechini process") using citric acid has also been applied to the synthesis of BaTi0,,"-'3 and Ba-p~lytitanate'~ in order to control the stoichiometry and to lower the processing temperature. However, the formation of a dense and rigid resin intermediate of citric acid and ethylene glycol, which leads to hard crystallite agglomeration during the pyrolysis, has been found to be a critical problem of the original Pechini appr~ach.'~ In the present study, our primary attention was paid to the formation of soft and porous intermediates in order to obtain reactive and stoichiometric fine powders without the use of esterification agents, such as ethylene glycol. As noted pre- viously,'6-20 the chelating ability of citric acid (a triprotic weak acid) and its complexation with metal ions are highly dependent upon the solution parameters such as pH, concen- tration, temperature, etc. It is necessary to investigate the chemical species present in an aqueous solution with respect to the solution parameters, especially solution pH. Hence, to optimize the preparation conditions of amorphous citrate precursors, we have carried out theoretical investigations, based on the thermodynamic equilibrium constants, on the solubilities to predict the behaviour of various chemical species in an aqueous solution.The present work is also concerned with the formation and evolution of crystalline Ba-polytitanates from the amorphous citrates precursors and the characterization of the resultant powders. Finally, the micro- wave dielectric properties of the densified BaTi,O, and Ba,Ti,O,, samples are also presented with a brief discussion of their sinterability and microstructure. Theoretical Consideration of Solubility Isotherms The characteristics of powders prepared by solution routes are highly dependent upon the chemical species present in the solution and the nature of the chemical species is also affected by the solution parameters. However, an empirical approach has generally been used to optimize the preparation con- ditions.With this point of view, a solubility isotherm that visualizes the stability domains of various chemical species, as a function of pH us. metal ion concentration (log[M"+]), may be very helpful for the determination of the optimum reaction conditions. Hence, the theoretical solubility isotherms for the BaC0,-citric acid-H,O and TiO(OH),-citric acid-H,O,-H,O systems were established as a function of the pH and concentration, based on the thermodynamic equilib- rium constants of the corresponding chemical species. The possible chemical species and their equilibrium constants considered in this study are summarized in Table 1. The same numerical algorithm as that in previous report^'^.'^ can be extended here, so the numerical details have been omitted.The resulting solubility isotherms for the BaC0,-citric acid-H,O system are shown in Fig. 1 as a function of log[Ba2+] and pH. At first, the possible species, which can be precipitated immediately as solid phases, are Ba(OH),(s) and BaCO,(s). The Ba(OH),(s) can be precipitated only in a fairly basic region (pH> 13) (point A). Instead of Ba(OH),(s), therefore, it is more reasonable to consider the BaC03(s) as a stable solid phase under atmospheric environments J. MATER. CHEM., 1995, VOL. 5 Table 1 Equilibria and their constants used in this calculation equilibrium reaction Ba(OH),(s) =Ba2++20H ~ Bat+ +H20=BaOH'+ +H+ BaC03(s)=Ba2++2C032-Ba2++C03'-=BaCO,'(aq) Ba2++C6H7O7'-=Ba(C6H7o7)" Ba2+f C6H6072-=Ba(C6H607)' symbol" Ks1 PI * KSZ K PI P2 Ba2+ +C6Hs073- =Ba(C6H507)'-TiO(OH),(s) =Ti02++20H-P3 Ks3 Ti02++H20=TiO(OH)'+ +H+ 81* Ti02++2H20=TiO(OH),'(aq)+ 2H+ P2* 8Ti02++12H20=(TiO),(OH),24++ 12H+ P812* TiOZ++H202=TiO(H202)'+ K Ti02++C6H5073- =TiO(C6Hs07)'- Ti02++2C6H5073-=TiO(C6H507)4-PI TiOZ++C6H707'- =TiO(C6H7O7)l+ P2 Ti02++2C,H7o7l-=TiO(C6H707)20 83 P4 ~~ log(constant) ref.-2.30 21 -13.47 21 -8.29 22 -5.49 22 0.60 23 1.48 23 2.95 23 -27.9 24 -1.60 24 -4.10 24 -1.68 24 4.0 25 11.90 26 6.36 27 2.91 27 5.40 27 a K, =solubility product; K =normal stability constant; =overall stability constant; P* =overall stability constant representing protolytic equilibria. PH 4 6 a 10 12 14 Fig.1 Distribution and solubility isotherms of Ba-containing species versus pH in the BaC0,-citric acid-H,O system (PCo2=10-3.5). The solubility isotherm of BaCO,(s) alone shows that the precipitation starts at pH ca. 7 (point B) when [Ba"] =0.1 mol dm-, and the predominant soluble species are free Ba2+ below pH 9 (point C) and BaCO,'(aq) above pH 9, respectively. However, when citric acid is present as a chelating agent, the solubility of BaCO,(s) increases due to the formation of soluble Ba-citrate complexes such as Ba(C6H607)'+, Ba(C&o7)' and Ba(C6H,0,)1-. The total concentration of soluble Ba-citrate complexes (= [Ba(C6H707)' '1 -t[Ba(C6H607)'] +[Ba(C6H@7)'-]) at equilibrium with a solid BaC03(s) is also shown in Fig.1. When the citric acid present in Ba2+-containing aqueous solution, Ba2 + preferentially forms complexes with citric acid, so that the precipitation of BaCO,(s) does not occur until the pH reaches 8.7 (point D). Citrate is the dominant soluble species below pH 11 (point E), beyond this pH limit BaCO,'(aq) becomes the dominant soluble species. The distribution of various chemical species and the solu- bility isotherms of the TiO(OH),-citric acid-H202-H,O system are represented in Fig. 2. In an aqueous solution, Ti4+ is rapidly hydrolysed and precipitates out as TiO(OH)2 [or Ti(OH),] owing to its high size-to-charge ratio. In general, hydrogen peroxide, which avidly forms complexes with Ti4 +, is added to retard the hydrolytic precipitation. The effects of the H202 complex on the solubility of TiO(OH),(s) can be seen clearly from Fig.2. In the absence of H202, TiO(OH),(s) -0 -6-Fig. 2 Distribution and solubility isotherms of Ti-containing species versus pH in the TiO(OH),-citric acid-H202-H20 system precipitates immediately at pH 1 (point F), but the pH limit shifts to pH 3 (point G) in the presence of H202 (1.0 mol dmP3), indicating that the solubility of TiO(OH),(s) increases significantly owing to the formation of a soluble TiO(H202)2+ complex in the acid pH domain. When the citric acid is competitively involved in the complex-formation reaction, the titanium-citrate complexes are present and dominant at pH <8 (below point I) and the precipitation of TiO(OH),(s) becomes possible beyond pH 7 (point H).Therefore, the dominant soluble species distribution, with respect to pH, is Ti-citrates at pH <8 and TiO(OH),'(aq) at pH >9. Finally, by taking into account the dissociation of citric acid, it is desirable to work at pH>pK, (5.33)28 to ensure the complete dissociation of citric acid also, in order to obtain pure and stable citrate complexes of Ba2+ and Ti4+ the solution pH should be maintained at pH <8 and 2 <pH <6.5, respectively. Thus, it can be concluded that the optimum condition is pH ca. 6 for the formation of pure and stable metal citrate complexes without the formation of any second- ary phases, such as hydroxide or carbonate.Experimental Sample Preparation The citrate route was used for metal-organic precursor syn- thesis. The starting reagents used were high-purity Ba(NO,), J. MATER. CHEM., 1995, VOL. 5 (>99%) and TiC1,(>99%). A 0.1 mol dmP3 nitrate solution of Ba was prepared by dissolving barium nitrate in distilled water. A 0.1 mol dmP3 aqueous titanium chloride solution was prepared by mixing of TiC14( 1) and H,O, (30%)-contain-ing distilled water, to suppress the hydrolytic precipitation of TiO,, the Ti-content was then determined volumetrically by EDTA back titration with 0.1 mol dm-3 lead nitrate solution. To prepare aqueous Ba- and Ti-citrate solutions, weighed quantities of citric acid (C,H,O7.2H,O) were added to the aqueous nitrate and chloride solutions, respectively.The aque- ous citrate solutions were then intermixed to the correspond- ing molar ratio of BaTi,O,, Ba,Ti,O,, and BaTiSOll. After mixing, the solution pH was increased from 1 to 6 by adding 30% ammonia solution. The water was slowly evaporated off from solution at 80 "C and a colourless colloidal suspension was formed at first. Further heating, for 1-2 h, at 100-150 "C resulted in dark, coloured, amorphous citrate gels with high viscosity, which were then subjected to calcination at various temperatures. Sample Characterization Thermal reaction of the amorphous citrate precursors was performed under an ambient atmosphere by simultaneous thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analyses (DTA) (heating rate = 10"C min-I). Crystalline phase evolutions of calcined pow- ders and sintered disks were examined by X-ray diffractip (XRD) with monochromatic Cu-Ka, radiation (A= 1.5405 A).The specific surface areas (SSAs) of the calcined powders were also measured using a conventional three-point BET tech- nique with N, adsorption. The particle size and the mor- phology of the selected calcined powders and the grains of the sintered samples were observed by means of scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was also used to examine crystallite size, shape and the degree of agglomeration. Microwave Measurement of Dielectric Properties The dielectric properties of the microwave frequency were measured by the resonant cavity method in the TEols dielectric resonator mode.,, In the measurement, disk-shaped samples with 1.2-1.4 mm thickness and 6-10 mm diameter were used.The unloaded Q-values were calculated from the resonant frequency curves. The temperature dependence of the resonant frequency (q)was measured in the range from -30 to 80°C. The relative permittivity (8,) was determined by an approxi- mate calculation method, using the resonant frequency in the TE,,, mode and the dimensions for the disk specimens as proposed in the literat~re.~' Results and Discussion Thermal Analyses The thermal decomposition of citrate precursor of Ba,Ti,O,, is shown in Fig. 3. At ca.100°C there is weight loss with TG and an endothermic peak with DTA due to the dehydration of free water. Between 250 and 290 "C an endothermic reaction takes place again with a second stage weight loss, which corresponds to the dehydration of citric acid to aconitic acid (Ba, Ti-C,H,O,) with the decarbonation of aconitic acid to itaconate (Ba, Ti-C6H,04)." The slight weight loss and the negligible exothermic peak with DTG and DTA at ca. 370 "C are probably due to the formation of itaconic anhydride (C&03) and the subsequent decomposition into C02 and H20. In the range 400-7OO0C, strong exothermic peaks with DTA and drastic weight losses with TG and DTG were 1 I I I 1 I I I I I I I 0 200 400 600 800 1000 TI'C Fig. 3 TG/DTG/DTA curves for the amorphous citrate gel precursor of Ba,Ti,O,, observable due to the vigorous combustion reactions of the residual organics.It is therefore expected that the decompo- sition might proceed as follows: (Ba, Ti)-itaconate 370-600 "C -BaC03, CO,, H,O, (BaC03)x.(Ti02)y 600-700 "C -BaTi,O,, , BaTi03,....., + CO, Crystallization Behaviour Fig. 4(a) shows the evolution of crystalline phases of citrate- derived BaTi,O, powders with different heat-treatment con-ditions. The citrate gel obtained was amorphous up to 700°C after which crystallization begins. After calcining at 700 "C for 1 h [Fig. 4(a)], only BaTi,Oll was observed. However, as the calcination temperature was raised up to 900 "C the reflection intensity of the BaTi,Og phase was drastically enhanced, indicating that the crystallization of BaTi,09 takes place rapidly even at a significantly lower temperature.After firing at 1200 "C for 1h, almost monophasic BaTi,O, was apparent with a trace of Ba2Ti902,, which both resulted from the decomposition of BaTi,O,, at around 1100"C. Monophasic BaTi,O, with orthorhombic symmetry could be obtained after sintering at 1300°C for 2 h. Fig. 4(b) shows the changes in the X-ray diffraction patterns of the Ba,Ti,O,, powders after calcining at different heating conditions. X-Ray phase analysis confirms the formation of poorly crystalline BaTi,O, , on heating the citrate precursor at 700 "C for 1 h [Fig. 4(b)]. The diffraction peaks show considerable broadening, indicating that the crystallite size is very fine.Calcination at 900°C for 1 h leads to a mixture of BaTi,Oll as the major phase and BaTi,O, as the minor one. However, after heating at 1100°C for 1 h it converts to a mixture of Ba,Ti,O,, and BaTi,O,, implying that the Ba,Ti,O,, phase begins to crystallize as the BaTi,O,, com-pound starts to dissociate at around 1100°C. The single- phase Ba,Ti,O,,, with triclinic symmetry, was formed when sintered at 1300°C for 2 h. From the above results, it seems that the diffusion of constituent elements is not the main factor controlling the formation of Ba,Ti,O,, as suggested previou~ly.~~The low rate of formation of Ba2Ti902, can be explained more reasonably by its higher surface and interface energies, compared with those of BaTi,O, or BaTi,O,, as .~~proposed by Wu et ~1The faster formation of Ba2Ti902, in our process is certainly due to the higher content of BaTi,01,,32 i.e., the higher the degree of compositional homo- J.MATER. CHEM., 1995, VOL. 5 n 1300"CI2h /I II llOO°C/lh 1 1 0 700 "C/1h A I I I I I I I I 1 I I I I I I I I 26 28 30 32 34 26 28 30 32 34 7OO0C/12h 01 0 70O"Ctl h 01 I I I I I I I I I 26 28 30 32 34 2Bldegrees Fig. 4 Powder X-ray diffraction patterns of citrate-derived BaTi,O, (a), Ba,Ti,O,, (b)and BaTi,Ol, (L') powders as a function of calcination temperature. 0,BaTi,O,; .,Ba,Ti,O,,; 0,BaTi,O,,; *,TiO,. geneity, the greater the amount of BaTi5011 formed in the calcined powder. The presence of BaTi50,, in the calcined powder facilitates the formation of Ba,Ti,O,, because of their similar structure of oxygen packing and because of the reduced volume change during transformation.The structural evolution of citrate-derived BaTi,Ol1 precur- sors with different firing conditions is shown in Fig. 4(c). After thermal decomposition of the citrate precursor at 700 "C for 1 h, almost monophasic BaTi5011 was formed immediately. Prolonged heating (12 h) at 700°C led to a single-phase BaTi5OI1 with monoclinic symmetry. However, the BaTi,O,, phase quickly decomposed into BaTi,09, Ba,Ti,O,,, and TiO, beyond 1050 "C for 2 h or hot pressed at 1050°C for 24 h under 8.4 MPa. These results are not consistent with those of previous report~,~,',~~ indicating that BaTi5011 is the stable phase under these firing conditions.Although the low stability of citrate-derived BaTi,O,, powders has not yet been com- pletely delineated, our best estimation at this stage is that the instability is strongly correlated with the particle character- istics after pyrolysis of the citrate precursors, the very fine particles with large reactive surface area could be the most effective factor for producing single-phase BaTi,O, powder whilst maintaining the high SSA. Maintaining the high SSA, however, also activates the decomposition of the BaTi5011 phase into BaTi,O,, Ba,Ti,O,, and TiO,. Particle Characteristics The particle characteristics of citrate-derived powders are summarized in Table 2. The particle size and shape for the J.MATER. CHEM.. 1995, VOL. 5 Table 2 Characteristics of citrate-derived particles BaTi,O, Ba,Ti,O,, BaTi,O, crystallization temperature/T ca. 900 ca. 1100 ca. 1100 SSA (SBEr/m2 g-') 55.7 49.7 52.4 ESD" /nm ca. 24 ca. 26 ca. 24 particle shape( TEM ) nearly round nearly round nearly round particle size(TEM)/nm 30-50 30-50 30-50 crystallite sizeb/nm ca. 36 ca. 35 ca. 35 a ESD =equivalent spherical diameter: D =6/(px SBET). Estimated by the Scherrer formula:33 f =(0.9ju)/(Bcos Q), where 1.= 1.5405 A and B= broadening of diffraction line measured at half its maximum intensity (in radians). powders calcined at 700°C for 1 h were observed by TEM (Fig. 5). The calcined powders consisted of nearly round individual particles with a diameter of 30--50 nm. The crystal- lite size was estimated as ca.30-40 nm by the effect of X-ray peak broadening using the Scherrer formula,33 which is con- sistent with that estimated from the TEM observations. After calcining the citrate precursors at 7OO0C, the SSAs were 50-56 m2 g-', corresponding to equivalent spherical diameter of 24-26 nm. The slight discrepancy between the particle size estimated by BET and that by TEM might be attributed to the surface roughness of the particles and to the assumption of perfect spherical geometry. Comparison of the particle sizes estimated by TEM, BET and X-ray peak broadening indicates that the calcined pow- ders are composed of monodispersive, nanometer-sized par- ticles.Such a result confirms that the citrate route is fairly effective for producing non-agglomerated fine particles with- out the use of esterification agents, such as ethylene glycol. Fig. 6 shows the particle morphology of the BaTi,O, powder heated at 700°C for 1 h. It can be seen from Fig. 6 that the spherically shaped particles are slightly necked each others, implying that grain growth takes place even below 700 "C. Sintering and Microwave Dielectric Properties The sintering behaviour and the microwave dielectric proper- ties of the BaTi,O, and Ba,Ti,Ozo powders prepared by the citrate route were investigated, and the results are summarized in Table 3. When the calcined BaTi,Og powder was die-pressed and fired at 1250°C for 10 h, the pellet could attain >96% of the theoretical density. The cross-sectional view of the sintered samples, which is composed of uniformly sintered grains of 3-8 pm, could be observed by scanning electron microscopy [Fig.7(a)]. The sample sintered at 1300 "C for 4 h shows a relatively low theoretical densification of ca. 9370, which indicates that the soaking time was not sufficient to achieve a fully densified specimen. The loss factor (Q) of the sample sintered at 1250°C for 10 h is larger than that of the sample sintered at 1300°C for 4 h. The difference in relative density resulted in the difference in Q-values, indicating that H30 mi H0.1 pm Fig. 5 Transmission electron micrographs of citrate-derived BaTi,O, Fig.6 Scanning electron micrograph of BaTi,O, powder calcined at (a), Ba,Ti,O,, (h)and BaTi,OIl (c) powders calcined at 700 "C for 1 h 700 "C for 1 h J. MATER. CHEM., 1995, VOL. 5 Table 3 Microwave dielectric characteristics of the sintered BaTi,O, and BazTi,Oz, BaTi,O, Ba,Ti,O,, sintering conditions/"C;h 1250;lO grain size/pm 3-8 relative density (%) 96.2 relative permittivity (c,) 36.2 loss factor (Q) 4900 measured frequency (fo)/GHz 10.3 Q xfo product 50500 1temperature coefficient (z,)/ppm "C-15.9 Prepared by conventional solid-state reaction from TiO, and BaCO,. Fig. 7 Scanning electron micrographs for the fracture surfaces of sintered BaTi,O, (a) and Ba,Ti,Ozo (b)samples poorer sinterability with higher structural defects, such as porosity and abnormal grain growth, could diminish Q.It is worth noting here that the Q-value of the sample sintered at 1250°C is one of the largest one among those reported so far for BaTi,O, measured in the frequency range of 10 GHz. For Ba,Ti,O,,, the powders obtained by both the citrate route and by the conventional method were sintered at 1200°C for 10 h in order to compare sinterability and dielec- tric properties. Under these conditions neither of the powders could be fully densified, but it was found that the citrate- derived powder could be sintered better than the conven-tionally processed one. Among the dielectric properties of these two samples, a distinct difference was found in the temperature stability factor, zf.The zf of the sample prepared by conventional route shows a very large positive coefficient (ca. 60 ppm OCP1),while the sample obtained by the citrate route represents an ideal zf value (ca. 0 ppm "C-'). The large 1300;4 1200;lO 1200;10" 1300;2 2-3 93.1 88.7 80.4 94.8 36.8 28.1 32.2 36.5 3850 3835 3685 5300 8.4 8.9 9.0 10.7 32500 34100 3 3 200 56800 8.2 -0.9 60.3 -6.2 zf value might originate from the existence of unreacted TiO, (rutile, zf=400 ppm "C-'), which depends greatly on the compositional homogeneity of powders and the particle reac- tivity. Raising the temperature above 1300 "C improves the compaction significantly, with a maximum relative density of ca. 95% being achieved within 2 h.Uniformly developed grains of 2-3 ym in size can be seen in the SEM photograph of the fracture surface, as shown in Fig. 7(b). As expected from the sinterability data, excellent microwave dielectric properties, E, =36.5, Q =5300 at 10.7 GHz and zf = -6.2 ppm "C-',could be obtained when the firing conditions were 1300°C for 2 h. The values obtained are also the best among those reported so far on ceramics with identical compositions, measured in the frequency range of ca. 10 GHz. Conclusions Nanometer sized (30-50 nm) barium polytitanates powders with high surface activities were prepared by the citrate route. The optimum pH condition (pH 6) for the formation of pure and stable metal citrate complexes was estimated based upon the theoretical consideration of solubility isotherms. The crystallization temperatures of BaTi,O, and BaTi,O, could be significantly reduced by sintering precursors with very reactive surface areas and good compositional homogeneities.However, the formation of the Ba,Ti90,0 phase seems to be controlled by its surface and interfacial energies not by the diffusion of constituent metal ions. The BaTi,09 and Ba2Ti9OZ0 samples with >95% theoretical density, fired at 1250 "C for 10 h and 1300"Cfor 2 h, exhibit excellent dielectric properties (E, =36.2, Q =4900 at 10.3 GHz, zf =15.9 ppm "C-and ~,=36.5, Q=5300 at 10.7GHz, zf= -6.2 ppm 'C-', respectively). The research is supported in part by the Korean Science and Engineering Foundation (92-00-25-02).References 1 S. Nomura, K. Toyama and K. Kaneta, Jpn. J. Appl. Phys., 1982, 21, L624. 2 S. Nomura, Ferroelectrics, 1983,49,61. 3 H. M. O'Bryan, J. K. Plourde, J. Thomson and D. F. Linn, J. Am. Ceram. SOC.,1974,57,450. 4 J. K. Plourde,D. F. Linn, H. M. O'Bryan and J. Thomson, J. Am. Ceram. 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ISSN:0959-9428    

DOI:10.1039/JM9950500057

出版商:RSC    

年代:1995

数据来源: RSC