摘要:

THE ROYAL SOCIETY OF CHEMISTRY Journal of Materials Chemistry Scientific Editor Staff Editor Professor Anthony R. West Mrs. Janet M. Leader Department of Chemistry The Royal Society of Chemistry University of Aberdeen Thomas Graham House Meston Walk Science Park Aberdeen AB9 ZUE, UK Cambridge CB4 4WF, UK Assistant Editor: Mrs. S. Youens Editorial Secretary: Miss D. J. Halls Graphics Designer: Ms. C. Taylor-Reid Materials Chemistry Editorial Board Anthony R. West (Aberdeen) (Chairman) Peter G. Bruce (St. Andrews) H. Monty Frey (Reading) C. Richard A. Catlow (London) John W. Qodby (Hull) David A. Dunmur (Sheffield) Brian J. Tighe (Aston) Jean Etourneau (Bordeaux) Allan E. Underhill (Bangor) Wendy R. Flavell (UMIST) John D. Wright (Canterbury) International Advisory Editorial Board M.A. Alario-Franco (Madrid, Spain) A. J. Leadbetter (Daresbury, UK) K. Bechgaard (Copenhagen, Denmark) J. S. Miller (Salt Lake City, UT, USA) J. D. Birchall (Runcorn, UK) P. S. Nicholson (Hamilton, Canada) D. Bloor (Durham, UK) M. Nygren (Stockholm, Sweden) A. J. Bruce (Murray Hill, USA) Y. W. Park (Seoul, Korea) A. K. Cheetham (Santa Barbara, USA) V. Percec (Cleveland, OH, USA) E. Chiellini (Pisa, Italy) N. Plate (Moscow, Russia) D. Coates (Poole, UK) C. N. R. Rao (Bangalore, India) P. Day (London, UK) M. Ratner (Evanston, IL, USA) B. Dunn (Los Angeles, USA) J. Rouxel (Nantes, France) W. J. Feast (Durham, UK) R. Roy (University Park, PA, USA) A. Fukuda (Tokyo, Japan) J. L. Serrano (Zaragoza, Spain) D.Gatteschi (Florence, Italy) J. N. Sherwood (Glasgow, UK) J. B. Goodenough (Austin, TX, USA) J. Simon (Paris, France) A. C. Griffin (Hattiesburg, USA) J. F. Stoddart (Birmingham, UK) S-i. Hirano (Nagoya, Japan) S. Takahashi (Osaka, Japan) P. Hodge (Manchester, UK) J. 0. Thomas (Uppsala, Sweden) H. lnokuchi (Okazaki, Japan) G. J. T. Tiddy (Bebington and Salford, UK) W. Jeitschko (Munster, Germany) Yu. D. Tretyakov (Moscow, Russia) 0. Kahn (Orsay, France) J. W. White (Canberra, Australia) M. Lahav (Rehovot, Israel) R. Xu (Changchun, China) Journal of Materials Chemistry (ISSN 0959-9428) is published monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts SG6 IHN, UK.NB Turpin Distribution Services Ltd., distributors, is wholly owned by The Royal Society of Chemistry. 1994 Annual subscription rate EC (inc. UK) f381.00, USA $718.00, Canada f431.00 (plus GST), Rest of World f410.00. Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003. USA POSTMASTER: send address changes to Journal of Materials Chemistry, Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003.Second Class postage paid at Jamaica, NY 11431. All other dispatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe. PRINTED IN THE UK. 0The Royal Society of Chemistry, 1994. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers. Professor A. R. West, Scientific Editor Mrs. J. M. Leader, Staff Editor Tel.: Aberdeen (0224) 272918 Tel.: Cambridge (0223) 420066 Fax: (0224) 272938 E-Mail (INTERNET): Telex: 73458 UNIABN G RSCl@RSC.ORG Fax: (0223) 420247 or 423623 Telex: 818293 ROYAL G Advertisement sales: Tel.+44 (0171-287 3091; Fax +44 (0)71-494 1134 INFORMATION FOR AUTHORS The Royal Society of Chemistry welcomes submission of manuscripts intended for publication in two forms, Articles and Materials Chemistry Communications. These should describe original work of high quality dealing with the synthesis, structures, properties and applications of materials, particularly those associated with advanced technology. 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 is normally acceptable. Four copies of Articles includ- ing a top copy with figures etc. should be sent to The Editor, Journal of Materials Chemistry, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK.Materials Chemistry Communications Materials $hemistry Communications con- tain novel scientific work in short form and of such importance that rapid publication is warranted. The total length is rigorously restricted to two pages of the double-column A4 format. The manuscript will be returned for reduction if this length is exceeded. For a Communication consisting entirely of text and ten references, with no figures, equations or tables, this corre-sponds to approximately 1600 words plus an abstract of up to 40 words. 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 submit- ted, 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. In order to avoid delay in publication, proofs of Communications are not sent to authors unless this is specifically requested. Full details of the form of manuscripts for Articles and Materials Chemistry Communications, conditions for accept-ance etc. are given in issue number one of Journal of Materials Chemistry published in January of each year, or may be ob- tained from the Staff Editor. There is no page charge for papers pub- lished in Journal of Materials Chemistry. Fifty reprints are supplied free of charge. Any author who is publishing in Journal of Materials Chemistry is entitled to a free copy of the issue in which the paper appears.

ISSN:0959-9428    

DOI:10.1039/JM99404FX013

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Dirhodium(ii) Tetraacetate Catalysed Hydroboration of Alkenes A New Route to Cyclic lodonium Ylides Photochemical Production of Tetravalent Americium in Hydrogencarbonate-Carbonate Media New Methods for the Synthesis of Perfluorooxaziridines Electron Tunneling in Heterogeneous Catalysis. Superoxide Anion Radical Decay on Palladium Promoted Yttria Subsequent Peripheral Cyclopropanation as a Synthetic Approach to Cyclic and Cyclo-substituted Triangulanes Total Synthesis of the Archaebacterial C,,-Diol and its Enantiomer Based on (R)-5-Acetoxy4-methylpentano~cAcid An Efficient Synthesis of (S,Z)-Dodec-3-en-ll-olide (Ferrulactone /I)* using 2-CarboxyethyltriphenylphosphoniumBromide Reaction of Trichloromethylarenes with Pyridine: A Novel Synthesis of N-(4- Pyridyl)pyridinium Salts and Aromatic Aldehydes Photochromic Behaviour of Non-transition Metal Chelate Complexes of Salicylaldimines Synthesis of Chromophores Based on Porphyrins and Open-chain Polypyrroles 3,4-Dinitrofuroxan-the First Example of a Pernitro Heterocycle New Intercalation Compounds of Molybdenum Disulfide with Transition metals Lower Oxidation States of Protactinium Photoionisation and Photoluminescence of Luminol in Aqueous Solution A Novel Mononuclear Tungsten(v/) Complex with 1-Hydroxyethylenediphosphonic Acid, Exhibiting a W03 Core Pressure Tensor and Local Density Profiles of Computer-simulated Water Clusters Registration Method for Metastable Decomposition of Benzene-Arn and Toluene-Arn Cluster Ions in RETOF Instruments Unusual Isotope Effect Induced by Photolysis of Uranyl Salts in Micelles Synthesis of Fluorinated 4H -1,4-Benzothiazine-2-carboxylic Acid 1,l-Dioxides-Thionated Analogues of Pefloxacin Natural Abundance Solid State 2H NMR Studies of Phase Transitions in Rotator Phase Solids Giant Pd Clusters observed by High Resolution Electron Microscopy

ISSN:0959-9428    

DOI:10.1039/JM99404BX015

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

ISSN 0959-9428 JMACEP(4) 501-652 (1994) Journal of Materials Chemistry Synthesis, structures, properties and applications of materials, particularly those associated with advanced technology The first six papers in this issue were submitted in association with the 1st International Conference on Materials Chemistry held in Aberdeen in July 1993. CONTENTS 501 Neutron scattering investigation of hydrogenic species in the ammonium molybdenum bronze (NH,),~,,H,.,,MoO, R. C. T. Slade and H. A. Pressman 509 AC and DC electrochemical investigation of protonic conduction in calcium-doped barium cerate ceramics R. C. T. Slade, S. D. Flint and N. Singh 515 Studies of the spinel solid solution Co,Ru, -xFe,O, M. H. Mendonqa, M. R. Nunes, F. M. A. Costa, A. Carvalho and M.M. Godinho 519 Oriented microporous film of tetramethylammonium pillared saponite M. Ogawa, M. Takahashi, C. Kato and K. Kuroda 525 Ge-doped bismuth vanadate solid electrolytes: synthesis, phase diagram and electrical properties C. K. Lee, M. P. Tan and A. R. West 529 Preparation and characterization of heavy-metal oxide glasses: Bi,O,-PbO-B,O,-GeO, System V. C. Solano Reynoso, L. C. Barbosa, 0. L. Alves, N. Aranha and C. L. Cesar 533 Chromic materials. Part 1.-Liquid-crystalline behaviour and electrochromism in bis(octakis-n-alkylphthalocyaninato)lutetium(rrr) complexes T. Komatsu, K. Ohta, T. Fujimoto and I. Yamamoto 537 Discotic liquid crystals of transition-metal complexes T. Komatsu, K. Ohta, T. Watanabe, H. Ikemoto, T. Fujimoto and I. Yamamoto 541 Anderson-type ammonium hexamolybdotungstonickelates P.Porta, G. Minelli, G. Moretti, I. Pettiti, L. I. Botto and H. J. Thomas 547 Cation ordering in distorted perovskites (MLa)(MgTe)O,, M=Na, K M. L. Lopez, M. L. Veiga and C. Pic0 551 Intercalation of organic compounds in the layered host lattice MOO, H. Tagaya, K. Ara, J-i. Kadokawa, M. Karasu and K. Chiba 557 FTIR and Raman spectroscopic investigation of 2,2’-bipyridine adsorption on silica, alumina, zirconia and titania S. A. Bagshaw and R. P. Cooney 565 Studies of the sorption of triethyl phosphate by ion-exchanged smectite clays C. J. Williamson and P. O’Brien 571 X-Ray analysis of two phases in the barium borate, sodium barium borate and sodium borate ternary phase diagram J.Bedson, R. W. Lawrence and P. J. Picone 575 Preparation, structure and magnetic properties of a new nickel(m) oxide: YbSr,NiO, M. James and J. P. Attfield 579 Oxygen diffusion in YB~,CU,O,_~ mixed conductors: interpretation of T-jump measurements and experiments on hysteresis of conductivity F. Cellucci, D. Gozzi and M. Tomellini 585 Effect of preparation methods on properties of alumina/titanias M. Toba, F. Mizukami, S-i. Niwa, Y. Kiyozumi, K. Maeda, A. Annila and V. Komppa 59 1 Effect of salt concentration on the properties of poly [oxymethy1ene-o1igo(oxyethy1ene)]/Mg(C10,), polymer electrolytes J. H. Thatcher, K. Thanapprapasr, S-i. Nagae, S-M. Mai, C. Booth and J. R. Owen 599 Synthesis of a new family of comb polymers with side-chain esters and ionic conductivities of their films containing lithium trifluorome- thane sulfonate Y. Takebe, K.Hochi, T. Matsuba and Y. Shirota 605 Selective removal of silicon from zeolite frameworks using sodium carbonate R. Le Van Mao, S. Xiao, A. Ramsaran and J. Yao 611 Effect of composition on the lattice parameters and thermal behaviour of nickel(r1)-cobalt(r1) hydroxide nitrate solid solutions K. Petrov, N. Zotov, E. Mirtcheva, 0. Garcia-Martinez and R. M. Rojas 615 Preparation of ZnO-based varistors by the sol-gel technique G. Westin, A. Ekstrand, M. Nygren, R. Osterlund and P. Merkelbach 623 Synthesis and characterization of poly(ary1 ether-sulfone) and poly (tetrahydrofuran) (A-B), block copolymers L. Zhao, R. S. Mani, T. L. Martin, J. Mueller and D.K. Mohanty 63 1 H,S-sensitive thin film fabricated from hydrothermally synthesized SnO, sol M. Ando, S. Suto, T. Suzuki, T. Tsuchida, C. Nakayama, N. Miura and N. Yamazoe 635 Photochromic behaviour in the fluorescence spectra of 1,2-bis( 9-acetoxy-10-anthry1)ethanein silicate glass prepared by the sol-gel method T. Fujii, H. Yamamoto and K. Oki 641 Study of the Ru-Mo-0 and Ru-W-0 phase systems; rutile solid solutions Ru,-,M,O, N. J. Stedman, A. K. Cheetham and P. D. Battle 647 Novel synthetic pathway to Bi(Pb)-2223 phase with variable Ca: Sr ratio, Bi,,,Pb,,,Sr,,Ca,Cu,O,,: 1.85 dxd2.4 P. V. P. S. S. Sastry and A. R. West MATERIALS CHEMISTRY COMMUNICATION 651 Effect of drying temperature on the physical properties of titania aerogels C.J. Brodsky and E. I. KO i Cumulative Author Index ... 111 Conference Diary Note: Where an asterisk appears against the name of one or more authors, it is included with the authors’ approval to indicate that correspondence may be addressed to this person. COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (0)71-437 8656, Fax: +44 (0)71-287 9798, Telecom Gold 84: BUR210, Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society’s Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge.

ISSN:0959-9428    

DOI:10.1039/JM99404FP033

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Cumulative Author Index 1994 Abraham I., 185 Conway L. J., 337 Isoda S., 291 Minelli G., 541 Smart S. P., 35 Akimoto H., 61 Cook M. J., 209 Isozaki T., 237 Mirtcheva E., 611 Smith E. G.. 331 Aksay I. A., 353 Ali-Adib Z., I Aliev A. E.. 35 Alves 0.L., 389, 529 Ando M., 631 Angeloni A. S., 429, 437 Cook S. L., 81 Cooney R. P., 557 Copplestone F. A., 421 Costa F. M. A., 515 Darriet B., 463 Davidson I. M. T., 13 Ivanovskaya M. I., 373 James M., 575 Jimenez R., 5 Jimenez-Lopez A., 179 Jones D. J., 189 Jones J. R., 379, 385 Miura N., 631 Mizukami F., 585 Mohanty D. K., 623 Moretti G., 541 Morpurgo S., 197 Mueller J., 623 Smith J. M., 337 Smith M. E., 245 Snetivy D., 55 Solano Reynoso V. C., 529 Solzi M, 361 Sotani N., 205 Annila A,, 585 ap Kendrick D., 399 Ara K..551 Arai K., 275 Aranha N.. 529 Davies A., 11 3 Deazle A. S., 385 del Arco M., 47 Dennison S., 41 Depaoli G., 407 Jung K., 161 Kadokawa J-i., 551 Karasu M., 551 Kassabov S., 153 Kato C., 519 Murray K. S., 87 Nagae S-i., 591 Nakano H., 171 Nakayama C., 631 Neal G. S., 245 Spagna A., 431 Stedman N. J., 641 Styring P.. 71 Su Q., 417 Suckut C., 5 Armelao L., 407 Dhas N. A., 491 Katsoulis D. E., 337 Neat R. J., 113 Sundholm F., 499 Armigliato A,, 361 Diamond D., 145, 217 Kawamura I,, 237 Nicol I., 29 Sutherland I., 487 Arnold Jr. F. E., 105 AsakaN., 291 Drabik M., 265, 271 Drennan J., 245 Kennedy B. J., 87 King T., 1 Nishiyama I., 449 Niwa S-i., 585 Suto S., 631 Suzuki T., 631 Aspin I. P., 385 Eda K., 205 Kiyozumi Y., 585 Nomura R., 51 Suzuki Y., 237 Attfield J.P., 475, 575 Ekstrand A., 615 Klissurski D., 153 Nomura S., 171 Swindell J., 229 Auroux A. 125 Azuma K., 139 Baba A,, 51 Eldred W. K., 305 Ellis A. M., 13 Etourneau J., 463 Knowles J. C., 185 KO E. I., 651 Kobayashi T., 291 Nunes M. R., 515 Nygren M., 615 OBrien P., 565 Taga T., 291 Tagaya H., 551 Takahashi M., 519 Babu G. P., 331 Fitzmaurice J. C., 285 Kohmoto T., 205 Ogawa M., 519 Takano M., 19 Babushkin O., 413 Fleming R. J., 87 Komatsu T., 533, 537 Ohnishi K., 171 Takebc Y., 599 Bach S., 133 Flint S. D., 509 Komppa V., 585 Ohta K., 61, 533, 537 Takeda Y.. 19 Bachir S., 139 Fraoua K., 305 Kossanyi J., 139 Oki K., 635 Takczoe H., 237 Badwal S. P. S., 257 Frialova M., 271 Kouyate D., 139 Olivera-Pastor P., 179 Tan M.P., 525 Baetzold R. C.. 299 Fujii T., 635 KriStofik M., 271 Osterlund R., 615 Tetley L., 253 Baffier N., 133 Fujimoto T., 61, 533, 537 Kubono K., 291 Owen J. R., 591 Thanapprapasr K.. 591 Bagshaw S. A,, 557 Baiios L.. 445 Fukuda A., 237 Galikova t,, 265, 271 Kubranova M., 265 Kunitomo M., 205 Pareti L., 361 Parkin I. P., 279, 285 Thatcher J. H., 501 Thomas H. J., 541 Barbosa L. C., 529 Galli G., 429, 437 Kuroda K., 519 Parsonage J. R., 399 Thomas M. J. K., 399 Barton J. M., 379, 385 Ganguli P., 331 Kuwano J., 9 Patil K. C., 491 Thomson J. B., lh7 Battaglin G., 407 Garcia A., 3 11 Lahti P. M., 161 Pennington M., 13 Thorne A. J., 209 Battle P. D.. 421, 641 Garcia-Martinez O., 61 1 Landee C., 161 Pereira-Ramos J-P., 133 Tian M., 327 Bautista F.M., 311 Gatteschi D., 319 Laus M., 429,437 Perez-Jimenez C., 145 Toba M., 585 Bedson J.. 571 Gee M. B., 337 Lawrence R. W., 571 Petrov K., 611 Tomellini M., 579 Bertoncello R., 407 Gibson R. A. G., 393 Lawrenson B., 393 Pettiti I., 541 Tondello E., 407 Beveridge M., 119 Bigi S., 361 Gil-Llambias F-J., 47 Glomm B., 55 Lee C. K., 525 Leece C. F., 393 Pic0 C., 547 Picone P. J., 571 Torres-Martinez L. M., 5 Trigg M. B., 245 Bignozzi M. C., 429 Godinho M. M., 515 Lefebvre F., 125 Porta P., 197, 541 Tsuchida T., 631 Bond S. E., 23 Goodby J. W., 71 Le Goff P., 133 Pottgen R., 463 Urbana M. R., 31 1 Booth C.. 591 Gozzi D., 579 le Lirzin A., 319 Povey I.M., 13 Uzunova E., 153 Botto L. I., 541 Granozzi G., 407 Le Van Ma0 R., 605 Predieri G., 361 Van Grieken R., 499 Bradley R. H., 487 Gravereau P., 463 Li J., 413 Pressman H. A.. 501 Vancso G. J., 55 Branitsky G. A., 373 Brewis D. M.. 487 Grins J., 445 Guo Z., 327 Lightfoot P., 167 Lindback T., 413 Ramsaran A., 605 Raynor J. B., 13 Veiga M. L., 547 Vidgeon E. A., 390 Britt S., 161 Hamerton I., 379, 385 Lindgren M., 223 Rhomari M., 189 Wang H., 417 Brock T., 229 Harris F. W., 105 Little F. J., 167 Richards B. C., 81 Wanklyn B. M., 4t19 Brodsky C-. J., 651 Harris K. D. M., 35 Liu C-W., 393 Richardson R. M., 209 Watanabe T., 537 Bruce D. W., 479 Harris S. J., 145, 217 Liu S., 379 Rives V., 47 Watts J. F., 305 Bruce P.G., 167 Haslam S. D., 209 Liu-Cai F. X., 125 Robertson A. D., 457 Wen J., 327 Bryant G. C., 209 Buist G. J.. 379. 385 Hatayama F., 205 Heath R. J., 487 Lo Jacono M., 197 Lopez M. L., 547 Robertson M. I., 29, 119 Rockliffe J. W., 331 Wessels P. L., 71 West A. R., 5, 445. 457, 525, Cairns J. A., 393 Hector A. L., 279 Loubser G., 71 Rodriguez-Castellon E., 179 647 Campelo J. M., 311 Caneschi A., 319 Cao X., 417 Carlino S., 99 Carr S. W.. 421 Hermansson L., 413 Hickey E., 463 Higuchi A., 171 Hirose N., 9 Hitchman M. L., 81 Luna D., 311 Lund A., 223 Macklin W. J., 113 Maeda K., 585 Mahgoub A. S., 223 Rojas R. M., 611 Romanovskaya V. V., 373 Ronfard-Haret J-C., 139 Ross A., 119 Rowatt B., 253 West D., 1 Westin G., 615 Williams G., 23 Williamson C.J., 565 Winfield J. M., 29, 119 Carrazan S. R.G., 47 Hix G. B., 189 Mai S-M., 591 Rowley A. T., 285 Workman A. D., 13 Carvalho A., 515 Hobson R. J., 113 Maireles-Torres P., 179, 189 Roziere J.. 189 Xiao S.: 605 Cassagneau T., 189 Cellucci F.. 579 Cervini R.. 87 Cesar C. L., 529 Hochi K., 599 Hodby J. W., 469 Hodge P., 1 Holmes P. A., 365 Malet P., 47 Mani R. S., 623 Marcos M. D., 475 Marinas J. M., 311 Russell D. K., 13 Ryan T. G., 209 Sano S., 275 Sastry P. V. P. S. S., 647 Yamamoto H., 635 Yamamoto I., 61, 533, 537 Yamamoto O., 19 Yamazoe N., 631 Challier T., 367 Cheetham .4.K., 641 Holmgren A., 413 Hourd A. C., 393 Marks G., 399 Martin T. L., 623 Saydam S., 13 Shamlian S. H., 81 Yang H., 55 Yao J., 605 Chehimi M. M., 305 Howlin B.J., 379, 385 Matsuba T., 599 Shen D., 105 Yogo T., 353 Chen C., 469 Chen Q., 327 Hu Y., 469 Hudson M. J., 99, 113 Matsuda H., 51 Maza-Rodriguez J., 179 Sheng E., 481 Sheridan P., 161 Yoshizawa A., 449 Yu H., 327 Cheng S. Z. D., 105 Chevalier R., 463 Chiba K., 551 Chiellini E.. 429, 437 Hudson S. A., 479 Hughes A. E., 257 Huxham I. M., 253 Ikemoto H., 537 McCarrick M., 217 McGhee L., 29, 119 McMeekin S. G., 29, 119 Mellen R. S., 421 Sherrington D. C., 229, 253 Shimokawatoko T., 51 Shirota Y., 171, 599 Simon M., 305 Zarbin A. J. G., 389 Zhang W-r., 161 Zhao L., 623 Zotov N.. 611 Ciacchi F. T., 257 Imanishi N., 19 Mendonqa M. H., 515 Sinclair D. C., 445 Coles G. S. V.. 23 Connell J. E., 399 Conroy M.. 1 Imayoshi K., 19 Inada H., 171 Islam M.S., 299 Merkelbach P., 615 Metcalfe K., 331 Mills G. P.. 13 Singh N., 509 Slade R. C. T., 265, 367, 501, 509 i Conference Diary 1994 April 5-8 8th High Temperature Materials Conference (HTMC VIII) Vienna, Austria Professor K L Komarek, Institut fur Anorganische Chemie der Universitat Wien, WghringerstraRe 42, A-1090, Wien, Austria Tel: +43(222)-345-424; Fax: +43(222)-310-4597 April 5-9 20th Annual Meeting: Society for Biomaterials Boston, USA Rosealee M. Lee, Executive Director, Society for Biomaterials, 6518 Walker Street, Suite 215, Minneapolis, MN 55426-4215, USA. Tel: 612-927-8108; Fax: 612-927-8127. April 11-13 Microscopy of Composite Materials I1 Oxford, UK The Royal Microscopical Society, 37/38 St Clements, Oxford OX4 lAJ, UK April 11-14 Deformation, Yield and Fracture of Polymers Cambridge, UK Mrs Debbie Schorer, Conference Department (C406), The Institute of Materials, 1Carlton House Terrace, London SW1Y 5DB, United Kingdom Tel: 071-839-4071; Fax: 071-839-3576 April 24-28 The American Ceramic Society Annual Meeting Indianapolis, USA Meetings Secretary, The American Ceramic Society Inc., 757 Brooksedge Plaza Drive, Westerville, Ohio 43081-6136, USA Tel: 614-890-4700; Fax: 614-899-6109 April 25-29 International Conference on Metallurgical Coatings and Thin Films (ICMCTF-94) San Diego, USA ICMCTF-94, Dale C.McIntyre, Sandia National Laboratories -New Mexico Advanced Materials Laboratory, 1001 University Boulevard SE, Suite 100, Albuquerque, NM 87106, USA May 15-20 Seventh International Meeting on Lithium Batteries Boston, USA Dr H.Frank Gibbard, Duracell Inc., New Products and Technology Division, Duracell Worldwide Technology Center, 37A Street, Needham, MA 02194, USA May 15-20 ICPS’ 94 The Physics and Chemistry of Imaging Systems Rochester NY, USA The Society for Imaging Science and Technology, 7003 Kilworth Lane, Springfield, VA 22151, USA. Tel: 703-642-9090; Fax: 703-642-9094 May 24-27 EMRS 1994 Spring Meeting Strasbourg, France P. Siffert, EMRS, BP 20,67037 Strasbourg Cedex 2, France. Tel: (33188 10 6543; Fax: (33)88 10 6293. June 11-16 Inorganic Chemistry: Surface Organometallic Chemistry, Molecular Materials and Catalysis Davos, Switzerland Dr Josip Hendekovic, European Science Foundation, 1quai Lezay-Marnesia, 67080 Strasbourg Cedex, France.Tel: (33188 76 7135; Fax: (33188 36 6987 June 13-16 Science and Technology of Pigment Dispersion Luzern, Switzerland Dr A V Patsis, Institute for Materials Science, State University of New York, New Platz, NY 12561, USA Fax: 914-255-0978 June 14-17 Workshop on Polymer Blends and Alloys Luzern, Switzerland Dr A V Patsis, Institute for Materials Science, State University of New York, New Paltz, NY12561, USA Fax: 914-255-0978 June 20-22 16th International Conference on Advances in the Stabilization and Controlled Degradation of Polymers Luzern, Switzerland Dr A V Patsis, Institute for Materials Science, State University of New York, New Paltz, NY 12561, USA Fax: 914-255-0978 June 22-24 TMS 1994 Electronic Materials Conference Colorado, USA Tim Sands, Department of Materials Science and Mineral Engineering, Hearst Mining Building, University of California, Berkeley, CA 94720, USA Tel: 510-642-2347; Fax: 510-642-9164 June 29-July 4 8th CIMTEC: Forum on New Materials and World Ceramics Congress Florence, Italy 8th CIMTEC, PO Box 174, 48018 Faenza, Italy Tel: +546-22461, + 546-664143; Fax: +546-66-3362 July 3-8 15th International Liquid Crystal Conference Budapest, Hungary Professor Lajos Bata, Research Inst for Solid State Physics of the Hungarian Academy of Sciences, Liquid Crystal Department, H-1525 Budapest, PO Box 49, Hungary Tel: 36-1-169-9499; Fax: 36-1-169-5380 11 July 3-8 First European Conference on Synchrotron Radiation in Materials Science Chester, UK Professor G N Greaves, SERC Daresbury Laboratory, Warrington WA4 4AD, UK Tel: +44(0)925-603335; Fax: +44(0)925-603174 July 4-8 First Euroconference -Ceramic Oxygen Ion Conductors and Their Technological Applications Lake Windermere, UK Ms M Peacock, Conference Department (C435), The Institute of Materials, 1Carlton House Terrace, London SWlY 5DB Tel: +44 (0171 235 1391; Fax: +44 (0171 823 1638 July 4-8 20th International Conference on Organic Coatings Science & Technology Athens, Greece Dr A V Patsis, Institute for Materials Science, State University of New York, New Paltz, NY 12561, USA Fax: 94-255-0978 July 4-9 Materials and Mechanisms of SuperconductivityEZigh Tc.Grenoble, France M Cyrot, CNRS, 25 Avenue des Martyrs, 38042 Grenoble, Cedex, France July 6-8 Silicon-Containing Polymers Canterbury, UK Dr R G Jones, Centre for Materials Research, Chemical Laboratory, University of Kent, Canterbury, Kent CT2 SNH, UK Tel: +44 (227) 764-000 ext. 3544; Fax: +44 (227) 475-475 July 6-11 Reactivity in Organized Microstructures: New Materials Mont Sainte Odile, France Dr Josip Hendekovic, European Science Foundation, 1quai Lezay-Marnesia, 67080 Strasbourg Cedex, France. Tel: (33)88 76 7135; Fax: (33188 36 6987. 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Tel: +886-35-820064, 886-35-916801; Fax: 886-35-820247, 886-35-820262; E-mail: 740366@MRL.ITRI.ORG.TW Conference Diary 1995 August 19-25 Clays and Clay Materials Science Leuven, Belgium Professor P Grobet, Secretary Euroclay '95, Centrum voor Oppervlaktechemie en Katalyse, K U Leuven, K Mercierlaan 92, B-3001 Heverlee, Belgium December 10th International Conference on Solid State Ionics Singapore B V R Chowdari, Department of Physics, National University of Singapore, Singapore -0511 iv

ISSN:0959-9428    

DOI:10.1039/JM99404BP035

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(4), 501-508 Neutron Scatteringt Investigation of Hydrogenic Species in the Ammonium Molybdenum Bronze (NH,)o,,,Homo,MoO, Robert C. T. Slade* and Helen A. Pressman Department of Chemistry, University of Exeter, Exeter, UK EX4 4QD Incoherent inelastic neutron scattering (IINS) and quasielastic neutron scattering (QENS) have been used in investigation of the ammonium bronze (NH~)o.~~Ho.&~O~.The IlNS vibrational spectrum reveals the presence of NH: (in the interlayer region of the a-MOO, host) and hydroxy groups (in intralayer bridging positions as in the parent hydrogen bronze, H0.27M~03).Variable-temperature QENS measurements on instruments of differing elastic energy resolutions and differing ranges of elastic scattering vector magnitude have been used in investigation of motions of the NH; ion.Broadenings are observed in QENS spectra over a remarkably large temperature range. In analysis of all spectra it was necessary to invoke a variable ‘static fraction’ of hydrogen, this arising from the temperature-dependent defect structures associated with incomplete filling of NH: sites and consequent variations in local environment of NH: ions. Variations in the scattering law [S(Q,m)]at low temperature were consistent with reorientation of order >3 of a fraction of the NH: present and were fitted assuming a four-fold barrier. At higher temperatures, spectra were treated using the isotropic rotational diffusion model for those reorienting ions giving discernible quasielastic broadenings, this diffusion being consequent on interaction of rotations of low-energy barrier with lattice modes.The layered a-MOO, structure (Fig. 1) allows intercalation of reducing-power analysis to be H1.70+0.02M003; the method a wide range of species without drastic alteration of the oxide used involved dissolution in an excess of cerium(1v) host.’,’ Schollhorn found that ‘H,~,MoO,’ exhibits Brarnsted ammonium sulfate and back-titration against iron@) acidity and that it reacts with Lewis bases (L) to form novel ammonium sulfate, as described previo~sly.~ This compound types of intercalation cornpo~nd,~ L,H,., -,Moo,. He sug- and the other products in this study are air-sensitive. All gested that transfer of protons from the oxide lattice to the handling and storage of these materials was therefore carried Lewis base, to give LH+, takes place (the species LH’ being out in an 0,-free glove box and all water was deoxygenated equivalent to an alkali-metal cation).Blue orthorhombic prior to use. H,Mo03 (0.23<x<0.4) has H atoms located in intralayer Hl.,MoO3 was mixed with MOO, and water was added to positions, the structure (space group Cmcm) determined by form an aqueous slurry with a view to carrying out the neutron diffraction4,’ being illustrated in Fig. 1.Dickens et aL6 coproportionation reaction ( I).’’ reacted this phase with NH,(g) to obtain (NH4)o~,,H,~o,Mo03 aH,Mo03 +bMoO, =(a +b)H,Mo03; z =ay/i3a+b) ( 1)(from H0.31Mo03). Powder X-ray diffraction and reflectance FTIR spectra (in particular a weak line at 1400 cm-’ charac- The mixture (in mole ratio Hl.7Mo03:Mo03 to give product teristic of NHZ) suggest that NH; occurs in the interlayer with zzO.3, within the composition range of the blue ortho- region with little perturbation of the host layers, but no further structural studies have been undertaken.The motions of the ammonium ion have been studied using the techniques of quasielastic neutron scattering (QENS) in a wide variety of materials containing NHT, these including ammonium salts, insertion compounds, intercalates and pro- tonic conductors. We have previously reported the application of these techniques in investigation of the reorientations of NH; in the ammonium tungsten bronze (NH4)o.22W03,7 which is chemically related to the mixed ammonium/hydrogen molybdenum bronze of this paper.btL We now report (i) characterisation of the hydrogenic species C in (NH4)o~,,H,~,3Mo0, by incoherent inelastic neutron scat- tering (IINS) vibrational spectroscopy and (ii) investigation of the dynamical processes involving interlayer NH,f by QENS. Experimental Materials Red monoclinic H1.7M003 was prepared by the method of Sermon and Bond (hydrogen spillover).8 X-Ray powder diffractometry (XRD; Philips PW 1050 diffractometer, Cu-Ka ”t radiation) confirmed the product to be a single monoclinic L a phase. The formula of this compound was determined by Fig. 1 a-MOO, structure, represented in terms of vertex- and edge- sharing of MOO, octahedra.The filled circles show the intralayer 7 Neutron scattering experiments were carried out at the Institut sites partially occupied by hydrogen in orthorhombic (Cmcmi Laue-Langevin, Grenoble, France. H,MoO,. rhombic phase'') was heated in a sealed glass tube [sealing under vacuum accomplished with the aid of cooling in N2( l)] at 1OO'C for 14 days. The product was washed in 0,-free water and then dried under dynamic vacuum for 24 h. XRD and reducing-power analyses confirmed a single orthorhombic phase of composition H0~,,~0,02Mo03. NH,(g) was passed over the blue orthorhombic phase and the temperature of the reaction vessel was maintained at < 18 "C. The gas flow and temperature were maintained for 40 h to ensure complete reaction.6 XRD confirmed the pcoduct was a siFgle orthorhombic pbase with a= 3.840(2) A, b= 32.39(1) A, and c=3.725(1) A, in good agreement with Dickens et aL6 Kjeldahl-type analysis (for NHJ content) was used to establish the formula of the product.Dissolution of the sample (ca. 1 g) in an excess of 0.1 mol dm-3 NaOH(aq) was followed by boiling for 30 min. Ammonia evolved was absorbed by an excess of standard 0.1 mol dm-3 HCl(aq), which was then back-titrated against standard 0.1 mol dm-3 NaOH(aq) using methyl red as indicator. The formula of the mixed ammonium/hydrogen molybdenum bronze in this study was (NH4)0.24+0.01H0.03M003* Neutron Scattering Experiments Incoherent Inelastic Scattering (IINS) The IINS spectrum of (NH4)0.24H0.03M003 over the range 200-2000 cm-l was collected on the instrument INlBeF (energy resolution z8%) at the Institut Laue-Langevin (ILL, Grenoble), the sample being contained in an aluminium slab- shaped can and held at a T <20 K (by use of a standard ILL cryos tat ).Incoherent Quasielastic Scattering (QENS) QENS spectra were recorded at the ILL using the back- scattering spectrometer IN13 and the focusing time-of-flight spectrometer IN6. Samples for neutron studies were sealed in slab-shaped A1 cans (window thicknesses 0.1 mm) of rectangu- lar (IN13) or circular (IN6) cross-section, using In wire gaskets and A1 nuts and bolts. Sample cans were inclined at 135" to the incident beam. Sample thicknesses were chosen to give < 10% scatter of the incident beam.Sample temperatures were controlled to+ 1 K using standard ILL cryostats. IN13 Measurements. Measurements on IN13 were made with an elastic energy resolution AEo=8 peV (fwhm) aqd over an elastic scattering vector magnitude range 1.19 <Qel/A-' <5.02. Spectra were recorded over an energy window of -75 to + 75 peV. Data acquisition times were typically >24 h. Empty can and vanadium (a similarly mounted V sheet sample) spectra were recorded (at 80 K over the same energy window) for use in data reduction and analysis. Temperatures at which quasielastic scattering data were to be collected were determined using constant-energy window experiments. In such an experiment the monochromator is held at a constant temperature equal to that of the analyser crystal and thus only neutrons of zero energy transfer are detected (i.e.only neutron intensity in the elastic channel is measured). In the absence of rotational or diffusive motions the elastic intensity I,, decreases gradually with temperature as a result of atomic vibrations (Debye-Waller attenuation). A more rapid decrease with increasing temperature takes place when discernible quasielastic broadening in the instru- mental energy window occurs. At still higher temperatures the quasielastic component broadens to become additional 'background' and a return to a less rapid decrease of elastic intensity takes place. The anticipated form of data from a constant-energy window experiment is thus a gradual decrease in elastic intensity at high and low temperatures, with a J.MATER. CHEM., 1994, VOL. 4 1 0 60 120 180 i7K Fig. 2 Constant-energy window experiments for (NH,)o,24H,,o,Mo0,. Elastic intensities (Iel) are normalised to the same monitor count. steeper decrease (a 'step') when quasielastic broadening would be discernible. The experimental results for (NH4)o~,4Ho~03Mo03are shown in Fig. 2. QENS spectra as a function of Qel were recorded at 105 and 115 K and were summed in pairs in order to improve the counting statistics at each temperature. IN6 Measurements. Measurements used an incident neutron wavelength Lo =5.1 A ando scattering vector magnitudes for elastic scattering Qel<2.1 A- (at a scattering angle 8, Qel= 47r sin O/&).Data acquisition times were typically 2 h. The experimental Q,,-dependen t resolution function was deter-mined using a similarly mounted vanadium sheet sample, and cadmium and empty-can scatterings were also determined. Quasielastic scattering spectra as a function of Qel were recorded at seven temperatures: 119, 151, 175. 200, 225, 260 and 295 K. Data Reduction. After subtraction of background and empty- can scattering (and Cd scattering in the case of IN6), scattering spectra were corrected for absorption and slab geometry and converted to the symmetrised scattering law S(Q,co)form (all steps using standard ILL procedures), where Q is the scat- tering vector. Results IINS Vibrational Spectrum The spectrum for (NH4)o~,4Ho~03Mo0, is shown in Fig.3. The antisymmetric and symmetric deformations of NH; are evi- dent at 177 meV (1420 cm-l) and 207 meV (1660 cm-l), respectively. The hydrogen positions in the parent blue orthorhombic H,Mo03 (0.23<x <0.4) have been defini-tively shown (by diffraction studie~~~~) to be in intralayer Mo, -0-H groupings (Fig. 1), the in-plane deformation of which leads to an intense peak at 157 meV (1260 cm-l) in the IINS spectrum of that compound. The peak at 152 meV (1220cm-') in the IINS spectrum in this study of (NH4)o~,4Ho~o,Mo03can similarly be assigned to deformation of Mo,-0-H. The strong scattering at 35 meV (280 cm-') and 50 meV (400 cm-') is due to torsional motions of NHZ. The peak at ca.75 meV (600 cm-l) and the broad scattering at 80-120 meV (640-960 cm-') cannot be definitively assigned, but combinations and overtones are likely in IINS spectra. As we have reported for the related hexagonal ammonium tungsten bronze (NH4)o.22W03,11 the spectrum in the energy range 110-170 meV (880-1360 cm-l) lacks any features assignable to the presence of NH, molecules (which could otherwise have intercalated as neutral molecules). It might be argued that the feature at 152 meV (assigned above J. MATER. CHEM., 1994, VOL. 4 503 wavenumber/crn-’ 0 440 880 1320 1760 2200 ,j 50 100 150 200 250 energy transfedme\/ Fig. 3 Inelastic neutron scattering spectrum for (NH4),~,4H,,,3Mo03 at T<20 K by us to to deformation of Mo,-0-H) is sufficiently broad possibly to be more than one overlapping band (and hence a contribution from a small quantity of neutral ammonia mol- ecules).It is, however, no broader than the peaks at higher energy transfers that are assigned to deformations of the NH: ion, and the instrumental energy resolution is low (CU.8%). It follows from the discussion above that the the hydrogen environments in (NH4)0.24H0.03M003are (i) in NH: formed on intercalation and (ii) in intralayer hydroxy groups as in the parent hydrogen bronze (Fig. 1).The ammonium ions will be in interlayer positions, as there are no sufficiently large intralayer sites. QENS Spectra The approach adopted in initial examination of all experimen- tal spectra was the same.Spectra were fitted individually to a simple analytical form, consisting of a simple scattering law S(Q,a)= Bo(Q)d(o)+F(QP) (2) convoluted with the instrumental resolution function. The quasielastic component F (Q,co)was taken to be adequately represented by a single Lorentzian (L).The empirical elastic incoherent structure factor [EISF, Ao(Q)]is the ratio of the elastic to the total (elastic +quasielastic) intensity in the incoherent scattering spectrum. Ao(Q)=Bo(Q)/(Bo(Q)+JF(Q,a)da) =Bo(Q)for normalised S(Q,w) (3) and is a measure of the time-averaged spatial distribution of the proton (incoherent scattering being dominated by the ‘H present), while the time-dependent proton position is in the quasielastic term F(Q,w). Scattering vector magnitudes Qel corresponding to Bragg scattering (diffraction giving a coherent elastic contribution) by the sample were determined from XRD data.In experi-ments using IN6, spectra from detectors ‘contaminated’ by Bragg scattering were simply ignored. In experiments using IN13, Ao(Q)(EISF) values at Qel ‘contaminated’!y coherent scattering (Qel=3.198, 3.524, 3.840, 4.134, 5.072 A) were cor- rected following Richardson et ~1.~~3’~ IN 13 Spectra Spectra at 105 and 115 K were found to have Qel-independent half-widths for the quasielastic (Lorentzian) component, con- E 0 , , , 2, , , 4, ,>1 3, 56 Fig. 4 Empirical EISF obtained on IN13 for ( NH4)0,24H,,03Mo03at 115 K. Vertical lines denote error bars. Solid lines show the predicted variations of EISF with Qelfor a range of possible reorientations (see text) of all of the NH; ions present.sistent with broadening originating in a reorientational motion (of NH:).14 Quasielastic broadening was small at 105 K, and spectra at 115 K were therefore used to extract Ao(Q) (the EISF). The intensities of the broadened components remained low, and this combined with the scatter in the individual spectra to give considerable (but unsystematic) scatter in the half-widths. In evaluating the empirical EISF (Fig. 4) spectra were fitted with the half-width for the Lorentzian fixed at the mean value (7 peV). IN6 Spectra Quasielastic broadening was observed at all temperatures. At each temperature the half-width for the quasielastic (Lorentzian) component was found to be QJndependent, consistent with broadening originating in a reorientational motion (of NH:).I4 The temperature dependence of half- widths was slight, but they did increase with temperature.Empirical EISF us. Qelplots showed a temperature dependence of Ao(Q),this being illustrated in Fig. 5. Consideration of Common Features The various spectra observed for both compounds have the following features in common: (i) Quasielastic broadening originating in reorientation of constitutional NH: is observed over a remarkably large temperature range. This is evidence for facile reorientation within the interlayer region of the SI-MOO, host (Fig. 1). (ii) Empirical EISF us. Qel plots show a temperature dependence.‘Theoretical’ variations of EISF with Qel can be calculated for various classical models of KHT ion jumping between different orientations within an essentially static host matrix (see below and Fig. 4). Empirical EISF values are higher than the corresponding ‘theoretical’ ones, indicating a higher elastic contribution in the empirical spectra. The compound in this study will have incomplete filling of NH,f sites in the interlayer region of the x-MOO, host framework (Fig. 1). Fig. 6 shows a projection (onto the y= 0.25 plane) of the interlayer region in the ammonium molyb- denum bronze, (NH4)o~24Ho~o,Mo0,,in this study [assuming the Cmcm space group of the parent orthorhombic Ho,27Mo0, to be retained on reaction with NH,(g)].Projection of the terminal O(3) atoms (Fig. 1)definFs an approximately square grid [a=3.840( 2) A, c =3.725(1)A]. A possible location for the ammonium ions would be in sites in cavities defined by four O(3) atoms (two from a layer above y=0.25 and two from the layer below), which are at the centres of the ‘squares’ J. MATER. CHEM., 1994, VOL. 4 in the projection of Fig. 6 and are of type 4c in Cmcm. The stoichiometry would then require 0.24 of these sites to be occupied. The local environment (and reorientatioiial barrier) for any given NH,f would then depend on how many neigh- bouring cavities were filled (assuming random occupation, this would range from zero to eight), each different arrange- ment causing a different perturbation of the layerv (and local vibrations of them) and a different electrostatic (NH;-NH;) contribution.Those (higher barrier) ions reonenting too slowly to produce discernible quasielastic broadening would give rise to purely 'elastic' scattering. The temperature depen- dence of the EISF may therefore result from a tzmperature- dependent distribution of NH: ions. Low activation barriers, as evident for NH: in this study, are commonly associated with the occurrence of non-classical phenomena (e.g. tunnelling). In the high-temperature limit large fluctuations in the potential barrier (due to interactions of rotations with thermal lattice vibrations) can even result in the observation of non-Arrhenius behaviour [such as the decreasing half-width of the quasielastic component at the highest temperatures in our study of (NH4)o.22W037].As discussed above, the variations in the half-widths for the quasielastic broadenings point to the observation of reorien- tational motions. A dissociation of NH:, in which hydrogen would transfer to a neighbouring terminal oxygen of the MOO, layers of the host, might also be thought possible. Those H-atom sites are, however, not those occupied by H in the parent hydrogen bronze (Fig. 1). Such a dissociation has been detected by 'H NMR in the related bronze (NH4),W0,,15716 in which the dissociation leads to long-range translation of the H that has transferred. That motion is strongly activated and at a timescale that would not give rise to quasielastic broadenings discernible with available instru- mentation (i.e.broadenings would be very much less than the instrumental resolutions). A similar dissociative mechanism, if present in the bronze in this study, would (1) not lead to broadening analysable as a reorientation (a rapid translational -0.0 0.5 1:O 1.5 2.0 2.5 motion of H would ensue as in the interlayer region in the bronze H1.,Mo03'), (ii) not lead to the weak temperature a&-' dependence of the observed broadenings and (iii) not give Fig.5 Temperature dependence of the empirical EISF obtained on broadenings discernible in the experimental temperature IN6 for the (NH,)o,,,Ho,03M003.Data correspond to measurements range. at (top-to-bottom) 295,200 and 151 K.Solid lines show the predicted variations of EISF with Qel for a range of possible reorientations (see text) of all of the NH; ions present. Data Analysis Reorientation of Ammonium Ions Reorientational motions of the NHZ ion have been studied in a large range of compounds using various spectroscopic techniques, e.g. ref. '2*17-20 . Neutron studies support the description of the NH,' ion as tetrahedral with an N-H0 bond length of 1.1A, as determined in NH,ReO, by neutron diffraction.21 Classical reorientation of the ammonium ion t 0 0 involves jumping between different orientations within the potential due to an essentially static environment. In contrast, the non-classical case with low barriers in the high-fC0 temperature limit is treated as rotational difi~sion,~'.~~ ions being taken to perform continuous small-angle rotations.Several literature studies of NH; reorientation are relevant to the further treatment of data in this study. Skold and 0 t 0 Dahlborgl7 studied NH4C1 and detected quasielastic broaden- ing (mean residence time on a site, qes=2 x 10-I2 s at 180 "C),rv 0 but they were unable to distinguish between two types of rotation (a two-fold jump about a C2 axis or a three-fold Fig. 6 Projection of the O(3) atoms neighbouring the interlayer rotation about a C3axis); the scattering laws for these models region in the a-MOO, structure (Fig. 1) onto the plane y=O.25. Filled circles represent atoms from the layer above, and open circles those over the Qel range studied are similar. Livingstone et ~1.'~ from the layer below.Dots represent 'cavity' sites that might be detected a dominant rotational mechanism of four-fold reori- (see text). entation (z,,, =3 x lo-'' s at 373 K) about a C'' axis in NH,Br. occupied by NH; in (NH4)o~,4Ho~03Mo03 J. MATER. CHEM., 1994, VOL. 4 A study of NH,ReO, by Richardson and HowardL2 in the temperature range 120<T/K <300 observed three-fold rotation. Studies of the layered solid protonic conductor NH: p-alumina24-26 observed 44% of the NH: ions under- going three-fold reorientation (z,,, = s at 395 K) about a C, axis. Those ions not observed rotating were said to be strongly hydrogen bonded in other sites and not free to rotate (a ‘static fraction’).In our own study of NH: in the h-WO, framework7 (in the ammonium tungsten bronze (NH4)0.22W03 and the hexagonal polytungstate [(NH,)zO],~,,,WO,) it was necessary to invoke a ‘static fraction’ of NH,f ions, this arising from the temperature- dependent defect structures associated with incomplete filling of NH: sites (in the hexagonal tunnels of the h-W03 host). Variations in the scattering law at low temperature were consistent with a classical description of jump reorientation of NHZ (interchanging three or four of the H-atom positions) of a fraction of the ions present. At higher temperatures non- classical behaviour was detected (half-widths for the quasielas- tic components in scattering spectra decreased at the highest temperatures), this arising from interactions of rotations with lattice modes, and spectra were then treated using the isotropic rotational diffusion model.Reorientational Models Jump reorientations of NH; can be discussed in terms of jumping of H-atoms between equivalent sites on a circle (following Barnes2’). For a population reorientating about a single axis the scattering law is then in the form of eqn. (2) and (3) (convoluted with the instrumental resolution function) with (4) where B,(Qr)=N-’z0[2Qr sin(np/N)] cos(2nnp/N) (5) j,(x)=(sin x)/x for a powder sample, r is the radius (of gyration) of the circle, N is the number of sites and z,= z1sin2(~/N)/sin2(nn/N).z1 is the half-width at half-maximum (hwhm) in angular frequency for the first Lorentzian and is related to the mean residence time on a site qesby z,,, =z1[1-cos (2n/N)] (6) In the case of observation of distinct reorientating and static populations (e.g.rotation of NH: about a single ionic C3 axis does not move 25% of the H present) the predicted EISF [&(Q)] for QENS spectra is simply related to AFt(Q) appro-priate to the dynamic population [calculated via eqn. (2) and (4)] is given by +,rot) (7)A,(Q) =[patic +prot~;~t(~)]/(pstatic where Paticand Protare the (relative) magnitudes of the static and rotating populations. The case of uniaxial rotational diffusion corresponds to the limiting behaviour as N+m. The scattering law for isotropic rotational diffusionz3 (no preferred orientation) has the form of eqn.(2) (convoluted with the instrumental resolution function) with where B,(Qr)=(2n+ MXQr). (9) jn(x)is a spherical Bessel fuction of order n, r is the radius of gyration (of the sphere on which H atoms move), T,’= n(n+ 1)D, and Dr is the rotational diffusion coefficient. The series in eqn. (8) is rapidly convergent (higher terms are negligible) except for large radii of gyration. In seeking to characterise the motion leading to quasielastic broadening, and to avoid any preconceptions derived from a hypothesis of the structure (as yet undetermined) of this ammonium bronze, the following reorientations of guest NH; (within the layered a-MOO, host) have been considered. Model A: Three-fold reorientation about a single ionic C, axis (an NH bond) or two-fold reorientation about a Czaxis. The computed EISF variations for these two possibilities are indistinguishable. Model B: Reorientation moving all H atoms to equivalent positions.This is achieved either by jump reorientation occurring about all four ionic C3 axes or by two-fold reorientation about ionic C2axes (bisecting the bond angles). Model C: Four-fold reorientation about one or more ionic C2 axes. The H atoms visit the eight corners of a cube in this model. Model D: Uniaxial rotational diffusion about an ionic C3 axis (model A with N-co). Model E: Isotropic rotational diffusion. The corresponding ‘theoretical’ EISF us. Qel variations are shown in Fig. 4. Comparison of Model and Experimental EISFs IN13 Spectra Fig.4 allows comparison of the empirical EISFs with the empirical data as obtained on IN13 at 115 K. As discussed above, empirical EISF values are higher than the correspond- ing ‘theoretical’ values, indicating a higher elastic contribution in the empirical spectra. This is attributable to the occurrence of ‘static’ (higher barrier) ions reorienting too slowly to produce discernible quasielastic broadening and is a conse-quence of incomplete filling of cavity sites (see above). Modification of any of models A-E to include the presence of some ‘static’ ions raises the calculated EISF towards the IN13 values and the effects of such modifications are shown in Fig. 7. Models A and B, which both involve reorientations of order <3, remain inadequate to explain the observed EISF variation.The variations across the full Qelrange are consistent with the higher order reorientations C (four-fold), D (uniaxial diffusion) or E (isotropic diffusion). The experimental data at low temperatures are thus consistent with a proportion of the NH; present undergoing motion describable as a high- order reorientation. In Fig. 7 this would correspond to static fractions of 52, 40 and 60% for C, D or E, respectively. Here, as in later discussion, ‘static H’ includes the residual hydrogen 0.4- I I I I 1 0 1 2 3 4 5 6 QedA-’ Fig.7 Modelling the empirical EISF obtained for (NH,)o,,,H,,o,MoO, at 115 K on IN13. The modified models are as follows (with static fractions in brackets): A (30%) (---), B (49%) (---), C (52%) (-), D (40%) (-**.-), E (60%) (-*-) present in hydroxy groups in intralayer sites (see discussion of IINS spectrum above).The 4c sites at the centres of the 'squares' in Fig. 6 (actually 'cavity' sites, see above) lie on a crystallographc C, axis. Considering the nearest-neighbour O(3)s only, a 90" jump of an NH: ion with its ionic C, axis coincident with the crystallographic axis would take the ion to an orientation very nearly equivalent to that before the jump (but not exactly equivalent as a#c); the C2 axis could thus define an approxi- mately four-fold reorientational barrier (characterised by two slightly different reorientational barriers). The absence of a C3 axis from the interlayer region could be taken as evidence against the model being a uniaxial diffusion of type D.It is tempting to assign the NH: to the 4c sites and thus to assign the motion as of type C at low temperature (rather than type E), but such an assignment is beyond the scope of the data. IN6 Spectra The Qel values accessed in the studies on IN6 were G2.1 A-'. Combination of the variations in 'theoretical' EISFs in this Qel range with the necessity to describe a proportion of the H present as static leads to the conclusion that modification of any of models A-E (using an appropriate choice of 'static fraction') could lead to a satisfactory fit to the data over such a narrow Qel range. As discussed above, the reorientational barriers are small in these compounds.IN6 spectra should be treated as in the high-temperature limit (i.e.with broadenings arising from non-classical reorientation which should be mod- elled as isotropic rotational diffusion). EISF data from IN6 can then be compared to the predictions of model E modified to incorporate a static fraction of ammonium ions. Visual fitting enabled evaluation of the static fractions as a function of temperature (see Table 1). Fig. 8 shows the corresponding empirical and (modified) theoretical EISFs as a function of temperature. It is expected that EISF41 as Qel+l. The observed small deviations from this behaviour arise from unavoidable incomplete removal of multiple scattering effects in data reduction, which affects empirical EISF values at low Qel.Modelling the Scattering Laws Empirical S (Q,o)data were fitted to a convolution of the instrumental resolution function with scattering laws of the form S(Q,O)=U~(~)+~S"~(Q,~) ( 10) In the case of spectra from IN13 the rotational scattering law Srot(Q,o)for reorienting ions was in the form of eqn. (2) and (3) as appropriate to model C (uniaxial four-fold reorien- tation). In these spectra U corresponds to combination of the elastic scattering arising from (i) 'static' hydrogen (proportion Table 1 Rotational diffusion coefficients for the NH,f ion in ( NH4)0.24H0.03M003 T,IK static H (%)a D,,lWV Dr/lO" Tad2 s-' 29 5 38 99 1.5 260 42 93 1.4 225 47 77 1.2 200 52 64 1.0 175 60 56 0.9 151 70 55 0.8 119 82b 8b 0.13b "Percentage of the total hydrogen 'static' (see text).bImprecise owing to the large static fraction and very narrow quasielastic broadening. J. MATER. CHEM., 1994, VOL. 4 0.0 1 0.0 0.5 -10.00.0 0.5 1.o 1.5 2.0 QejA-' Fig.8 Modelling the temperature-dependent empirical ETSFs obtained for (NH4)o~24Ho,o,Mo03on IN6. Data correspond to measurements at (top to bottom) 295, 200 and 151 K. The model EISFs correspond to isotropic rotational diffusion of NH; ions, with incorporation of the temperature-dependent 'static' tractions of (top to bottom) 38, 52 and 70% of the hydrogen present (Table 1). determined above) and (ii) Bragg scattering (at known angles). Spectra were initially fitted individually as a function of Qel, yielding residence times zreS of (1.5 k0.5)x f 0-l' s (105 K) and (7.0f4.0) x 10-l' s (115 K).Fig. 9 present.; representative final fits (z,,, fixed to mean values) of S(Q,w) iks a function of Qel.The fits are satisfactory. In the case of spectra from IN6, the rotational scattering law Srot(Q,w)for reorienting ions was in the form of eqn. (2) and (8), as appropriate to isotropic rotational diffusion of reorienting ions (model E). In these spectra U corresponds solely to the elastic scattering from 'static' ions (proportion determined above). Spectra were initially fitted individually as a function of Qel,yielding the T-dependent mean rotational diffusion coefficients D,given in Table 1. Representative final fits (D,fixed to mean value at each T)of S(Q.w) as a function of eeland T are given in Fig.10. The fits are satisfactory. Discussion Temperature dependence of EISFs might be taken as evidence of a simple change in reorientational mechanism. The situation in these systems is, however, considerably more complex, with J. MATER. CHEM., 1994, VOL. 4 i ‘*-. 4.28 o 0.28 0.56i’Ii 1i ,_ic 1 -0.28 0 0.28 0.56 / . . . . . . .__... -* --\ -0.28 0 0.28 0.56-Fig. 9 Fitso to the scattering law S(Q,o)obtained on IN13 for (NH,)o,,,Ho,03Mo0, at (a) 105 and (b)115 K and (left to right) Qel = 1.29, 2.47, 4.13, 5.07 A-*. Solid lines show the fits to the data (+). Dashed lines separate the elastic and the quasielastic (broadened) components.a ‘static fraction’ evident in the low-temperature (IN13) spectra assigned to jump reorientation. The reorientational barrier for a probe NH: ion will be sensitive to the detailed local environment. The temperature dependence of the EISF is consequent on the non-stoichiometry of this system and is explicable in terms of a temperature-dependent distribution of ammonium ions in the interlayer region. If the ‘cavity’ sites of type 4c are used, this would correspond to a T-dependence of the relative populations of NH: with 0, 1, 2, 3, 4,5, 6, 7 and 8 nearest-neighbour cavities occupied. In this study and to a first approximation: (i) ions with no neighbouring cavity filled will all have similar barriers, (ii) the barriers will differ for each pattern of filling of neighbouring cavities. This system therefore presents complex theoretical problems.This study has yielded information concerning purely reori- entational motions of NH:. ‘H NMR detected two additional motions in the related bronze (NH4)xW03,15’16 these being a hopping of NH: between cavities in that material [a mechan- ism for changing the defect structure in both that material and in (NH4)o,24Ho~o,Mo0,] and a high-temperature (dissoci- ative) self-diffusion of H (discussed earlier). Those motions were very much slower in (NH,),WO, than the reorientations probed in this study and, assuming that similar timescales for such motions apply in (NH4)o~24Ho~o,Mo0,, would not give rise to quasielastic broadenings discernible with available instrumentation (i.e. broadenings would be very much less than the instrumental resolutions). Conclusions The IINS vibrational spectrum confirms the presence of NH; (in the interlayer region of the a-MOO, host) and J.MATER. CHEM.. 1994, VOL. 4 ated with the partial filling of NH; sites is suggested. Such behaviour would result in a distribution of activation barriers, lower barrier ions giving rise to discernible broadenings in quasielastic neutron scattering spectra S(Q,o) over a wide temperature range. Reorientational barriers associated with observed NH; ion reorientations in this material are low. Quasielastic neutron scattering spectra [S(Q,o]at low tem- perature are consistent with reorientation about a barrier of order >3 for a fraction of the NH: ions present, and have been treated assuming a four-fold barrier.Spectra at higher temperatures are treated using the isotropic rotational diffusion model for those ions giving rise to quasielastic broadening, such a diffusion being consequent. in the high- temperature limit, on interaction of rotations of low energy barrier with lattice modes. We thank the Institut Laue-Langevin for access to spec-trometers INlBeF, IN6 and IN13. We thank SERC for grants in support of the Exeter neutron scattering programme and for a studentship for H.A.P. References 1 R. Schollhorn and R. Kuhlman, Muter. Res. Bull., 1976,11,83. 2 R. Schollhorn, Angew. Chem. Int. Ed. Engl., 1980,19,983. 3 R.Schollhorn, T. Scutte-Nolle and G. Steinhoff, J. Less. Common Met., 1980, 71, 71. 4 F. A. Schroder and H. Weitzel, 2.Anorg. Allg. Chem., 1977, 435, 247. 5 P. G. Dickens, J. J. Birtill and C. J. Wright, J. Solid State Chem., 1979,28, 185. 6 P. G. Dickens, S. J. Hibble and G. J. James, Solid State lonics, 1986,20,213. 7 R. C. T. Slade, P. R. Hirst and B. C. West, J. Mater. Chem., 1991, 1,281. 8 P. A. Sermon and G. C. Bond, J. Chem. Sue., Farudaji Trans. 2, 1976, 72, 730. 9 R. C. T. Slade, P. R. Hirst and H. A. Pressman, J. Mater. Chem.. 1991, 1,429. 10 J. J. Birtill and P. G. Dickens, Muter. Res. Bull., 1978, 13, 3 11. 11 R. C. T. Slade, A. Ramanan, P. R. Hirst and H. A. Pressman, Muter. Res. Bull., 1988,23, 793. 12 R. M.Richardson and J. Howard, Chem. Phi's., 1984,86,235. 13 R. M. Richardson, A. J. Leadbetter, D. H. Bonsor and G. J. Kruger, Mol. Phys., 1990,40,747. 14 M. BCe, Quasielastic Neutron Scattering: Principles and Applications in Solid State Chemistry, Biology und Muterials Science, Adam Hilger, Bristol, 1988, ch. 6. 15 L. D. Clark, M. S. Whittingham and R. A. Huggins, J. Solid State Chem., 1972,5487. 16 R. C. T. Slade, P. G. Dickens, D. A. Claridge, D. J. Murphy and T. K. Halstead, Solid State Ionics, 1990,38, 201. 17 K. Skold and U. Dahlborg, Solid State Commun., 1973, 13, 543. 4.40 0.00 0.40 0.80 ElmeV A 1-0.40 0.00 0.40 0.80 ElmeV I\ \-,0.40'0.00 0.80-0.40 ' ' 75zrTz-4.40 0.00 0.40 0.80 ElrneV Fig. 10 Representative fits to the temperature-dependent scattering laws S(Q,w) obtained on IN6 for (NH,),,,,Ho,,,MoO, at (left to right) Q,,=0.27, 1.13, 2.07 k'and (a) 151 K (70% static protons), (b)200 K (52% static protons) and (c)295 K (38% static protons).Solid lines show the fits to the data (+). Dashed lines separate the elastic and quasielastic (broadened) components. hydroxy groups (in intralayer bridging positions as in the parent hydrogen bronze, H,.,,MoO,). The interlayer region 'of the a-MOO, host constitutes an open environment for reorientation of NH,f ions. In this study, a temperature dependence of the defect structure associ- 18 T. Chakraborty, S. S. Khatri and A. L. Verma, J. Chem. Phys., 1986,84,7108. 19 R. C. Livingstone, J. M. Rowe and J. J. Rush, J. Chem. Phys., 1974,60,4541. 20 H. J. Prask, S. F. Trevino and J. J. Rush, J. Chern. Phys., 1975, 62,4156. 21 R. J. C.Brown, S. L. Segel and G. Dolling, Actu Crystnllogr., Sect. B, 1980,36,2195. 22 V. F. Sears, Can. J. Phys., 1966, 44, 1999. 23 V. F. Sears, Can. J. Phys., 1967,45234. 24 J. D. Axe, L. M. Corliss, J. M. Hastings, W. L. Roth and 0.Muller, J. Phys. Chem. Solids, 1978,39, 155. 25 J. C. Lasskgues, M. Fouassier, N. Baffier, Ph. Colomban and A. J. Dianoux, J. Phys. (Paris), 1980,41, 273. 26 J. C. Lassegues, in Solid State Protonic Conductors I, for Fuel Cells and Sensors, ed. J. Jensen and M. Kleitz, Odense University Press, Odense, 1982, p. 96. 27 J. 0.Barnes, J. Chem. Phys., 1973,58,5193. Paper 3/04206E; Received 19th July, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940400501

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM.. 1994, 4(4), 509-513 AC and DC Electrochemical Investigation of Protonic Conduction in Calcium-doped Barium Cerate Ceramics Robert C. T. Slade,*" Sara D. Flint" and Narendra Singh,"b a Department of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD Department of Physics, Gaya College, Gaya-823007, lndia Protonic conduction in barium cerates doped with a divalent metal, BaCe, -xCax03-, (x =0.02, 0.05, 0.10, 0.15), has been investigated at high temperature in a moist atmosphere. Conduction by protons was confirmed by emf measure- ments using specimen ceramics as the solid-electrolyte membrane separating moist and dry nitrogen atmospheres. Bulk electrical conductivity, ob, measurements were carried out using impedance techniques. Plots of log(o,.,T) versus 1/T showed apparent Arrhenius behaviour. Conductivity increases markedly with increasing x for 0 <x <0.05, but not for x 2 0.10.The protonic conductivity for a 10% Ca-doped ceramic at 900 "C is ca. 2 x 1OP3 S cm -' with an .activation energy' of 54 kJ mol-'. At high temperature, dc measurements for x =0.02 gave 'conductivities' approaching ob values obtained by impedance measurements, but contributions other than bulk resistance became increasingly significant at lower temperatures. Of those contributions, the electrode-electrolyte charge-transfer resistance was of particular importance. High-temperature proton-conducting solids are potentially useful materials for many electrochemical applications such as high-temperature fuel cells, hydrogen sensors and hydrogen gas separators.A decade ago Iwahara and co-~orkers'-~ found that certain perovskite-type oxide solid solutions (e.g. doped SrCeO,, BaCeO,) exhibit protonic conduction in an atmosphere containing hydrogen or water vapour at high temperature. There are many solids exhibiting high protonic conductivities, e.g. hydroxides, hydrates and acid-base but most are unsuitable for uses at high temperatures (>300 -C) because they decompose by liberating water. It is well known (e.g. refs. 9 and 10) that in barium cerate doped with trivalent metals (BaCe,-,M,O,-, [M=Y, Yb, La, Nd and Gd; x =0.05 and 0.10; r =x/2]) protons are generated by equilibrium between the doped perovskite and water vapour or hydrogen-containing atmospheres at high temperature.The oxygen vacancies which are produced by partial substitution of Ce by aliovalent metals (e.g. Y, Yb, La, Nd and Gd) therefore play an important role in the appearance of proton conduction. We now report an ac and a dc electrochemical examination of electrical conductivity of barium cerate containing Ca2+ as a divalent dopant, and an examination of the effect of dopant level. In the literature, purely Ca-doped materials have been mentioned briefly (Iwahara et d2),with a study of substitution by Ca in BaCe,.,Nd,.,O,-m (itself a doped material) also having been reported." In a paper in a symposium proceed- ings, Liu and NowickI2 concluded that Ca-doped BaCeO, is indeed a proton conductor, but their detailed measurements pertained to a low-temperature regime (25-200 "C).They also concluded, on the basis of the absence of an isotope effect, that dopants such as Gd lead to dominant conduction by oxide ions, but we have reported an isotope effect in that system at the higher temperatures of potential interest for device application.' Experimental The Ca-doped ceramic oxides were prepared by solid-state reaction of BaCO,, CaO (BDH Chemicals) and CeO, (Aldrich) in stoichiometric ratio according to: BaCO, +( 1-x)CeO, +xCaO-+BaCe, -,CaXO3 --a +C02 ( 1) x=O.O2, 0.05, 0.10, 0.15 and a=x The dried powdered raw materials were mixed, ground and then calcined in an alumina crucible at 1450T for 10 h in air. The resulting powder was wet (H,O) ground in a McCrone micronising mill for 20 min and dried overnight at 120nC. The product was pressed hydrostatically into pellets ca.16 mm in diameter and 1 mm thick and sintered in air at 1400°C for 10 h (producing pellets of typically 85590% of theoretical density). Platinum paste (Engelhard A4338) was applied to both pellet faces as electrodes; an intimate contact between electrolyte and porous Pt-electrode was ensured b), sintering at 1000°C for 10 h in air. Electrical conductivity measurements employed impedance techniques (5 Hz-1 MHz) with a Hewlett Packard 4192A LF impedance analyser, programmed via an IBM-compatible computer for data collection and analysis (employing EQUIVCRT modelling software,',).A specially designed elec- trochemical cell assembly14 with two compartments for separ- ate gas flow to each side of the specimen ceramic disc was used. A gold ring/high-temperature cement gasket provides the seal between compartments. The whole cell assembly was mounted horizontally in an electric tube furnace programm- able down to 1"C min-'. 'Wet' (bubbled through H20 at ambient temperature) and 'dry' (passed through an activated molecular sieve column) nitrogen gases were passed to differ- ent compartments of the cell. Emf and dc conductivity measurements were made with a Princeton model 173 potentiostat. The perovskite phases were charac terised by X-ray powder diffraction (Philips PW 1050 diffractometer modified for computer-driven step-scanning an( data acqui- sition; Ni-filtered Cu-Kcr radiation, i= 1.541 78 A).Results and Discussion X-Ray Powder Diffraction The X-ray diffraction (XRD) patterns of BaCe, -xCax03-or (x =0.02, 0.05, 0.10 and 0.15) confirmed single-phase perovsk- ite structures (without any unassignable lines in the XRD profiles of freshly calcined samples), the pattern for x=0.10 being shown in Fig. 1 (in which the inset shows the data replotted with a logarithmic intensity scale and confirms the phase purity). Patterns could all be satisfactorily indexed in terms of a cubic unit cell (space group Prnh). The literature in this area clearly demonstrates that such materials are indeed single phases (solid solutions), but there is considerable J.MATER. CHEM., 1994, VOL. 4 EMF Measurements Stable ends were measured using ceramic discs of BaCe, -xCax03-(x=0.02, 0.05, 0.10 and 0.15 ) as electrolyte membranes separating moist and dry nitrogen. The negative terminal was that for the wet compartment and the polarity of the cell reversed on interchanging the moist and dry gas flows. This behaviour of the cell is explicable only in terms of the ceramic diaphragm acting as a protonic conductor. The EMF arises from the different partial pressures of H20in the two-cell compartments and the following electrode reaction: H20 +2H+(electrolyte)+ QO,(g) +2e-(2) Impedance Spectra The impedance spectra of the ceramic discs were recorded after pretreatment in flowing moist nitrogen for ca.1 h at each temperature. Typical spectra for Ca-doped BaCeO, with x=O.O5 are shown in Fig. 2. Spectra are typical of the ionic motion in solids. At temperatures T < 600°C two depressed semicircles are evident, followed by a linear impedance vari- ation at lower frequencies. The higher- and lower-frequency arcs are incomplete owing to instrumental limitation of the experimental frequency range. The higher-frequency arc corre- sponds to phenomena occurring in the bulk of the electrolyte. This arc is displaced from the origin owing to the existence of unavoidable impedances related to cell design and which affect the spectra at higher frequencies. This becomes increas- ingly significant as the resistance of the sample decreases with increasing temperature.The lower-frequency linear impedance variation represents the behaviour occurring at the electrode/electrolyte interface. An arc was observed in the mid-frequency range. This can be assigned to grain-boundary impedances which arise from intergranular matter (which may differ in composition to the bulk), constriction resistance due to small areas of contact between the grains, and associated void space. The consequence of this, re-expressed in terms of electrical components, is an additional resistance and capaci- tance in parallel, which is then in series with the bulk resistance and the geometrical capacitance associated with the contacts -6000 (a)1-40001 -"""I 250 7, 510 4500 VJ -20 30 40 50 60 70 80 90C3 2gdegrees0 n confusion as to whether a cubic (Prn3rn),15316tetragonal (P4/mbn1),~'or orthorhombic (Pbnrn)18,19unit cell is the case (the unit-cell symmetry may even depend on the dopant level and temperature20'21); this confusion may be in part due to the sometimes-neglected sensitivity of this system to reaction with C02(g).22 XRD patterns alone are an insufficient basis for choosing a lower symmetry than cubic (combination of structural parameters and low scattering powers for light atoms leading to unobservable intensities in XRD profiles for lines that would characterise lower symmetry).Neutron diffraction studies [as in ref. 191 on pure samples, at a range of compositions, processing conditions and temperatures are needed if the structural chemistry in this system is to be definitively resolved.In Table 1 we present cell constants for the materials in this study on the assumption of cubic or orthorhombic unit cells. The 'cubic cell parameter' does not vary significantly with composition (x), and those for the 'tetragonal/orthorhombic' option show no systematic variation with x (this would not be surprising if the unit-cell symmetry were not constant across the composition range, see above). The question as to whether the Ca substitutes for Ba (the common substitution in many perovskite systems) or, as in the case of trivalent dopants, for Ce (the ionic radii for Ce4+ and Ca2+ being very similar) is an open one; if a cubic unit cell were true for the whole range, the former substitution could lead to a smooth variation in a with x (Vegard's law), while the latter could lead to only slight variations in a.This problem might be resolved by neutron diffraction studies, or by Ca EXAFS. Table 1 Alternative unit-cell constants for BaCe, -xCax03-a (see text) 0 2000 4000 TOO-7-0 250 500 750cubic cell :, 0" 4.397 1 (d)0.02 4.401( 1) -1 601 -4:0.05 4.400( 3) 0.10 4.397( 2) -1 20: -3 +0.15 4.395(4) orthorhombic cell 0" 6.235( 1) 8.78 1 (1) 6.212( 1) 0.02 6.225(2) 8.769(5) 6.207( 9) 0.05b O.lOb 6.206(5) 6.216(5) 8.740( 6) 8.82(4) 6.202( 9) 6.22(2) 0.15 6.236( 40 8.788(3) 6.219( 5) "Early work', (based on X-ray powder photographs) suggested a cubic unit cell which transforms to orthorhombic with increasing x in Sr,Ba, _,CeO,.More recent neutron powder diffraction studies" have indicated an orthorhombic cell. Processing conditions could play a significant role. bTetragonal within experimental error. -80' 7 53 1 -2: 5 3 Z '/Q Fig. 2 Impedance spectra of cells with BaCeo~,,Ca,~,,03 ~a as electro- lyte membrane. Decadic logarithms of the frequency of the ac stimulus (v/Hz) are shown adjacent to arrows indicating associated data points. (a) 391, (b)538, (c) 637, (d)847 "C. J. MATER. CHEM., 1994, VOL. 4 to the test-piece. The value of this ‘grain boundary resistance’ (Rgb) and the associated capacitance decreases with increasing temperature, as is evident from the spectra at higher temperatures.The equivalent circuit which represents the behaviour of the sample is shown in Fig. 3. The appearance of the impedance spectrum depends directly on the values of the individual electrical components; some of these values are temperature dependent, and hence so is the impedance spec- trum. All the experimental spectra were modelled using EQUlVCRT ~0ftware.l~Table 2 presents the temperature dependences of the values for circuit elements in a typical test -acell containing BaCeo,95Cao,05Ce03 and giving the impedance spectra presented in Fig. 2. Rb is the bulk resistance in parallel with the geometrical capacitance C, (C, z 100 nF at 300 < T/”C<600, but cannot be resolved at higher tem- peratures).Cgb and Rgb are, respectively, the grain boundary capacitance and resistance in series with the bulk resistance (c,b x 15pF at 300 < T/”C < 700). R,, represents the interfacial electrode-electrolyte charge transfer resistance, which occurs in parallel to the Warburg impedance (Zw,a diffusion-related impedance indicating mass transport phen- omena and arising from diffusion of H+ through a concen- tration gradient near the electrodes). The double-layer capacitance at the electrode-electrolyte interface (CCJwas not resolvable. Z, represents the unavoidable impedances associ- ated with cell design. AC Conductivity Ac conductivity was evaluated for BaCe, -,Ca,O, -a (x=0.02, 0.05, 0.10 and 0.15) in the temperature range 300d TCd 900 in moist N, (both compartments). Bulk electrolyte resist- ances Rb were evaluated from impedance spectra. Plots of log(obT) as a function of 1/T are shown in Fig.4. Similar data (to within 10%) were obtained for pellets of different thickness. The samples exhibit apparent Arrhenius-type T Rct Fig. 3 Equivalent circuit showing the electrical behaviour of cells with BaCe, pxCax03 -I as electrolyte membrane Table 2 Temperature dependence of circuit elements for a test cell containing BaCe,,,,Ca,~,,O, --a and giving the impedance spectra in Fig. 2 391 1804 50 1995 14 29000 1.3 47 1 699 63 304 13 2057 6.6 538 39 1 98 91 11 857 13 585 277 180 43 12 367 24 637 140 a 17 19 36 20 709 136 a 7 25 44 51 742 110 a a a 23 70 792 82 a a a 9.4 85 847 68 a a a 4.5 120 885 43 a a a 2.5 160 ~~~ “Could not be evaluated from the experimental impedance spectrum, the form of which was determined by other elements.0.0-Y v I E, CI) -1.0-i= b v cn0 --2.0-\ 0 -3.0 I I 1 1 S I 0.6 1.o 1.4 1.8 1O~WT Fig. 4 Temperature dependencies of ac conductivitieh, gb, for BaCelpxCax03--a with x = 0.02 (O), 0.05 (C),0.10 (+), 11.15 (0) dependences of conductivities, with ‘activation energies’ (corre- sponding to the plotted lines, obtained by linear iegression analysis within the Kaleidagraph data presentation software2,) of 54, 56, 54, 42 kJ mol-I for x=O.O2, 0.05, 0.10, 0.15. The charge carrier (H’) density is a function of Tin these materials (a consequence of the reaction between atmosphere and vacancies in the ceramic) and it follows that these kalues are not directly related to the activation energy of an atomic-level jump process.Conductivity for all samples is higher than for parent BaCeO,, which is not itself a proton conductor (the high concentration of oxygen vacancies introduced by doping is absent, and hence protonic charge carriers are not generated). Conductivity increases markedly with increasing x for 0 < x < 0.05, but not for x 3 0.10. The latter is perhaps not too surprising as the charge carrier density is considerably lower than the concentration of oxygen vacancies.’ The protonic conductivity for a Ca-doped sample with x=0.10 is ca.S cm-I at T= 800 “C, with an ‘activation energy’ of 54 kJ mol-’. In contrast, the conductivity (not protonic) of undoped parent BaCeO, at 800 “C is ca. S cm-’ [log(eT /S cm-’ K) z -1.0 at lo3 K/T=0.93].24 DC Cell Studies High-temperature (400 < 7°C < 800) dc studies were made passing moist nitrogen through both compartments of the cell. The relationships between applied voltage and current were ohmic, but currents were slow to stabilise (< 4 min at low temperature, increasingly rapid at higher temperatures). We assign the latter observation to equilibration of thc porous electrodes with the moist gas environment. Initial studies showed dc ‘conductivities’, capp,deduced from current -voltage relationships to be lower (typically a factor < 5) than bulk conductivities, cb, obtained by ac techniques (Fig.4). This is not unexpected as the ac impedance measurements were used to obtain the bulk resistance Rb of the sample, whereas the dc measurements sum the resistances in the equivalent circuit (Fig. 3). The dc resistance of a pellet therefore includes contributions from electrode polarisation, from charge-transfer resistance at the electrode/electrolyte interface RCt, and from the grain-boundary resistance Rgb. R,, and Rgb are low at high temperatures (see Table2), the latter being too low to measure. An in-depth investigation was carried out for x =0.02 (BaCeo.,8Cao~0203-,J. The temperature dependence of the current-voltage relationship is shown in Fig.5. The tempera- ture dependences of cappand the bulk (ac) conductivity, cb, 512 '200[ t1000 800 -600 -0 100 200 300 400 500 600 Vapdm" Fig. 5 Temperature dependence of the dc current-voltage relationship for a cell with BaCe,~,,Ca,,,,O,-, as electrolyte membrane. Lines correspond to measurements at (top-to-bottom) 800, 750, 701, 650, 601, 550, 400 C. are shown in Fig. 6. The ratio of oapp/obis strongly tempera- ture-dependent, as shown in Fig.7. oappvalues approach bb at high temperatures, but contributions other than the bulk resistance become increasingly significant at lower tempera- tures in dc measurements. As can be seen in Table 2, the electrode-electrolyte charge-transfer resistance, Rct, is -0.5--1.5-G-? I E cI) -2.5-i= -0 -3.5:I-4.5; I I I 1 0.9 1.1 1.3 1.5 1.7 ~O~WT Fig.6 Temperature dependencies of the 'conductivity', oapp(O), deduced from dc current-voltage relationships (Fig. 5) and ob (0) from impedance measurements, for a cell with BaCe,.,,Ca,.,,O, -n as electrolyte membrane 0.8'.OI Fig. 7 Temperature dependence of the ratio of the 'conductivity', oaPp,deduced from dc current-voltage relationships (Figs. 5 and 6) and the bulk electrolyte conductivity, ob, resulting from impedance measurements (Fig. 6) for a cell with BaCeo,98Cao,o,03-, as electrolyte membrane J. MATER. CHEM.. 1994, VOL. 4 dominant at low temperatures. The significant role played by electrode phenomena was also evident in the lengthened equilibration times at lower temperatures (discussed above), and could be due in part to the electrode reaction used (with H20 as the source of hydrogen).Others have, however, reported the conductivity activation energy in similar mate- rials to differ at high and low temperature^;^^ that observation may result from monitoring of phenomena other than bulk conductivity at low temperatures. For instance, the activation energy cited for Ca-doped BaCeO, by Liu and Nowick (cu. 75 kJ mol-'),12 and resulting from low-temperature measure- ments, is 50% higher than that found in this study (ca. 50 kJ mol-'). Our measurements extend down to 350'C. Direct comparison of the analysis of raw data in these two cases is prevented by the lack of either raw data or an equivalent circuit in Liu and Nowick's work.Concluding Remarks We have demonstrated that cerate ceramics containing a range of concentrations of divalent Ca as dopant are perov- skite-type single phases BaCe, -xCax03-n (x =0.02, 0.05, 0.10 and 0.15) and exhibit protonic conductivities in moist atmos- pheres at high temperature. Conductivity increases markedly with increasing x for O< x < 0.05, but not for .Y 3 0.10. The resistance of ceramic discs is high (slightly higher than in the case of rare-earth dopants), but resistances would be reduced considerably by using thin films of the cerates and could be usable in a solid oxide fuel cell (SOFC). The appearance of impedance spectra and the information that can be gleaned from them by modelling with an equivalent circuit are strongly dependent on the values (themselves temperature-dependent) of the individual components.Ca-doped BaCeO, is less conductive than analogous materials in which trivalent dopant metals are employed (e.g. ref. 14). Detailed investigation of both the ac and the dc electrochemi- cal behaviour of the Ca-doped materials in this study at T 2 350 "C has, however, led to considerably more information concerning the temperature-dependence of individual compo- nents than has been reported for more conductive cerates. The Exeter programme of investigation of proton-conduction in ceramics receives support from British Gas plc. We thank the Science and Engineering Research Council for a CASE studentship (jointly with British Gas plc) for S.D.F. References 1 H.Jwahara, T. Esaka, H. Uchida and N. Maeda, Solid State Ionics, 1981,314, 359. 2 H. Iwahara, H. Uchida, K. Ono and K. Ogaki. J. Electrochem. Soc., 1988, 135, 529. 3 H. Uchida, H. Yoshikawa and H. Iwahara. Solid StLife Ionics, 1989,34, 103. 4 T. Hibino, K. Mizutani, T. Yajima and H. Iwahara, Solid Stute Ionics, 1992,57, 303. 5 L. Glasser, Chem. Rec., 1965, 75, 21. 6 F. W. Poulsen, in High Conductivity Solid Ionic Conductors, ed. T. Takahashi, World Scientific, Singapore, 1988, pp. 166-200. 7 S. Chandra, in Superionic Solids and Solid Electrolytes, Academic Press, New York, 1989, pp. 185-226. 8 Proton Conductors: Solids, Membranes and Gels; Materials and Devices, ed.Ph. Colomban, Cambridge university Press, Cambridge, 1992. 9 R. C. T. Slade and N. Singh, J. Mater. Chem., 1991, 1,441. 10 N. Bonanos, Solid State Ionics, 1992,53-56, 967. 11 T. Yajima, H. lwahara and H. Uchida, Solid State Ionics, 1991, 47, 177. 12 J. F. Liu and A. S. Nowick, in Solid State Ionics 11,ed. G. A. Nazri, D. F. Shriver, R. A. Huggins and M. Balkanski. MRS Sjimposium Proceedings, 1991,210,675. J. MATER. CHEM., 1994, VOL. 4 513 13 14 15 16 B. A. Boukamp, Solid State lonics, 1986,20, 31. A. J. Smith and A. J. E. Welch, Acta Crystallogr., 1960,13,653. R. C. T. Slade and N. Singh, Solid State Ioylics, 1991,46, 11 1. N. Bonanos, B. Ellis, K. S. Knight and M. N. Mahmood, Solid 21 22 T. Scherban, R. Villeneuve, L. Abello and G. Lucazeau, Solid State Ionics, 1993,61, 93. M. J. Scholten, J. Schoonman, J. C. van Miltenburg and H. A. J. Oonk, Solid State Ionics, 1993,61, 83. 17 18 State lonics, 1989,35, 179. S. Shin. H. H. Huang, M. Ishigame and H. Iwahara, Solid State lonics, 1990,40/41,910. A. J. Jacobsen, B. C. Tofield and B. E. F. Fender, Acta Crystallogr., 23 24 Kaleidagraph data analysis/graphics application (fur the Macintosh series of computers), Version 2.0, Synergy Software, Reading, Pennsylvania, 1990. A. N. Virkar and H. S. Maiti, J. Power Sources, 1985,14,295. 19 Sect. B. 1972, 28,956. K. S. Knight, M. Soars and N. Bonanos, J. Muter. Chem., 1992, 2, 709. 25 T. Scherban, W-K. Lee and A. S. Nowick, Solid State Ionic s, 1988, 28-30,585. 20 T. Scherban, R. Villeneuve, L. Abello and G. Lucazeau, Solid State Commun., 1992,84, 341. Paper 3/04208A; Received 19th July, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940400509

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994,4(4), 515-517 Studies of the Spinel Solid Solution Co,Ru, -xFexO, M. H. Mendonqa; M. R. Nunes,a F. M. A. Costa,*aA. Canalhob and M. M. Godinhob a Departmento Quimica, Faculdade Ciencias, Universidade de Lisboa, I 700 Lisboa, Portugal Departmento Fisica, Faculdade Ciencias, Universidade de Lisboa, 1700 Lisboa, Portugal The substitution of Ru by Fe in the cubic spinel Co,RuO, has been studied for the system Co,Ru,-,Fe,O,. All the compounds are cubic spinels and are semiconductors with a certain degree of inversion. The variation of conductivity indicates that the incorporation of Fe decreases the concentration of free electrons. A ferrimagnetic spinel can be represented by the formula A [B2]04, in which A and B refer to metal ions placed in an oxygen tetrahedron or octahedron, respectively.If the tetra- hedral A and octahedral B sites are occupied by metal ions possessing a magnetic dipole moment, cooperative ferrimag- netic phenomena may be observed below a particular tempera- ture. The properties of these materials depend on what kind of metal ions are presented in the different sites and how they are distributed. Some studies of ferrimagnetic spinels’-3 and the attempt by Krutzsch and Kemmler-Sack4 to substitute Ru by Fe in the normal spinel Co2Ru0, have led us to the study of the system Co,RuO,. Previous reported different cation distri- butions for the spinel Co2Fe04, while studies on Co2Ru04 show a normal distribution for this pin el.^,^ The spinel systems with ruthenium and iron are at present unknown.With regard to the chemical behaviour of ruthenium and iron ions in octahedral coordination, it is important to study the ion-site competition and its effect on physical properties and chemical behaviour. In this work we have therefore prepared samples of the Co,Fe, -xR~x04 solid solu- tion and have studied its structural, electrical and magnetic behaviour in order to predict the effect of the iron and ruthenium ion competition on physical and chemical properties. Experimental A number of polycrystalline ferrite samples in the system CO~F~~-~~RU,O~(x=O.O, 0.2, 0.5, 0.8), were prepared by the standard ceramic powder method using analytical grade Co304, RuO, and Fe203. The reagents were mixed in an appropriate composition and then prefired for 6 h at 1073 K to avoid thermal decomposition of the oxides.After this step the samples were reground and fired at 1230K for several hours. The compounds were sintered at the same temperature for 24 h. This treatment was carried out in air in an appro- priate oven. Powder X-ray diffraction patterns were recorded in the range 28 =15 -85” range using a Philips X-ray diffractometer (PW 1730). Cu-Kr radiation was used for all the compounds. For all specimens, X-ray diffraction patterns showed only lines belonging to the cubic spinel structure. 57Fe Mossbauer spectra were carried out at 300K with a transmission spectrometer AME-50 (Elscint) operating at constant acceleration in conjunction with a 512 channel analyser.A commercial source with 25 mCi of 57C0 in a Rh matrix was used. The spectrometer was calibrated with thin absorbers of elemental iron and powdered a-Fe,03. The absorbers were prepared in the form of a uniform layer of the crystalline powder samples dispersed in an appropriate phenolic powder, without iron. Magnetic measurements were performed in a SQUID mag- netometer (Quantum Design, MPMS system) which allows the measurement of the magnetic moment in the teinperature range 2-400 K under fields up to 5.5 T. Electrical resistivity was measured by the van der Pauw method at temperatures ranging from 530 to 775 K. The four point probe contacts were of thin Pt wire, and the thickness of the samples was ca.1.5mm. Results and Discussion X-Ray Powder Diffraction All the samples were indexed as a single cubic phase as shown in Table 1, according to ASTM file no. 23-193. The structural refinement was done with the aid of the computer program LSUCRE. Cell parameters a, for the compounds of 1 he spinel system are presented in Table 2. The variation of the unit cell with x is not linelrr, and a maximum is obtained for the Co,Ruo,,Fe0~,O4 compound. Considering the a parameter, a certain degree of inversion (A) appears to occur, related to the cation distribution of partially inverted CO,F~O,.~ If we consider the Shannon and Prewitt7 effective ionic radius, we can verify th$t Co2+ in octahedral coordination has a high value (0.885 A) which is consistent Table 1 d spacing and h,k,I, for Co,Ru04 1 1 1 4.764 2 2 0 2.915 3 1 1 2.486 2 2 2 2.380 4 0 0 2.061 3 3 1 - 4 2 2 1.684 5 3 1 3 11 31 1.588 4 4 0 1.458 5 3 1 1.393 6 2 0 - 5 3 3 1.258 6 2 2 1.244 4 4 4 1.191 4.763 2.917 2.487 2.381 2.062 1.892 1.684 1.588 1.458 1.394 1.304 1.258 1.244 1.191 Table 2 a, Lattice parameter of the system Co,Ru,-,Fe,04 X aoIA spinel composition 0.0 (8.241 & 0.6) x C02Ru04 0.2 (8.259 f0.5) x Co,RuO,,,Fe,~,O, 0.5 (8.310k0.9) x Co,RuO,,,I~eo,,O, 1.0 0.8 8.254’(8.262f0.6) x Co,FeO,Co,RuO,.,,,o.,O4 “From F.K. Lotgering, Philips Research Reports, vol. 11, 1956p. 337, for comparison with cell parameter of the studied system.with the largest cell parameter for Co,Ruo.,Feo,504 and its possible degree of inversion. "Fe Mossbauer Studies Fig. 1 shows the transmission gamma spectra as a function of relative source-absorber velocity, obtained at room tempera- ture for all the compounds. The Mossbauer parameters of this system, relative to the source in the Rh matrix, are given in Table 3. As is well known, the Mossbauer isomer shift is related to the oxidation state of iron on the absorber and it has very different values when Fez+ is present rather than Fe3+. The I100.0----.~ ' I. " '-ti I 1I i 89.8 , -1 0.0 -5.0 0.0 5.0 10.0 100.0. . .. . J. MATER. CHEM., 1994, VOL. 4 isomer shifts obtained imply that Fe2+ is not present in the compounds studied.On the other hand, the presence of Fe3+ in spinel-type compounds gives a different value for the isomer shift according to its structural coordination. Analysis of the isomer shift gives values of 0.361 and 0.387 mm s-' typical of Fe3+ octahedral coordination for the x=0.2 and 0.5 com-pounds, respectively, and 0.259 mm s-' for the x=O.8 com-pound, which may correspond to some Fe3+ in tetrahedral coordination.* These results support the X-ray studies on Co2Ru0.5Fe0,504and the possibility of structural inversion of this compound. Magnetic Properties The magnetization was measured as a function of temperature for different applied fields, in the following way. The sample was first cooled from room temperature to 5 K in zero field, and the magnetization was then determined as a function of temperature from 5 to 380K [zero field charge (zfc)] and down to 5 K again [field cooled (FC)], under a measured magnetic field.Hysteresis curves were obtained for all the samples at different temperatures and with applied fields up to 5 T. The temperature dependence of the spontaneous magnetiz- ation for the three samples is shown in Fig. 2. Curie tempera- tures, obtained from the magnetization measurements, are plotted as a function of x in Fig. 3. The saturation -\i I'2%3010 I 82,5I-! I ., I !! -1 0.0 -5.0 0.0 5.0 10.0 :i2 01 I II I II 0 50 100 150 200 250 300 350 TIK Fig. 2 Magnetization as a function of temperature for x=(O) 0.2; (0)0.5; (A)0.8 L I,,, I...,,,.-1 0.0 -5.0 0.0 5.0 10.0 v/mm s-' Fig. 1 Mossbauer spectra for the spinel system Co,Ru, -xFe,O, obtained at room temperature: (a) C0,Ru0,,Fe,.,0,; (h)C02Ru0.5Fe0.504; (c) Co2RufJ.ZFe0.804 Table 3 Room-temperature Mossbauer parameters of the system Co,Ru,-,Fe,O, (relative to 57Fe in an Rh matrix) spinel composition 6/mm s-' A/mm s-' HIT CozRu,,,Fe,.20, 0.361 0.41 5 -CO~RU,~~F~,~,O,0.387 0.490 -CoZRu0,2Feo.804 0.259 -0.112 33.9 From ref. 7 (Fe3+)': 0.19<6/mm s-l ~0.35;(Fe3+)": 0.29 <b/mm s-l ~0.38;(Fez+)': 0.83 <6/mm s-'<O.94; (Fez+)": 0.98 <6/mm s-' < 1.13. 600 I 400 -Y \t2 200 ' 0 0.0 0.2 0.4 0.6 0.8 1.0 X Fig. 3 Curie temperature as a function of iron content (x) J.MATER. CHEM., 1994, VOL. 4 0.0 0.2 0.4 0.6 0.8 1.0 X Fig. 4 Saturation moment (0)and cell parameter (0)as a function of s Table 4. Curie temperatures obtained from the M(T) variation. Saturation, magnetization and remanence obtained from hysteresis curves at T= 10 K sample TJK M,/emu g-' M Jemu 8.' magnetization was obtained for each sample from the extra- polation (T=O) of the M(T) dependence; this value was checked by the extrapolation to H=O of the linear region in the hysteresis curves at low temperature. The values of the saturation moments (Fig. 4) confirm a degree of inversion for the samples, which was inferred previously from the cell parameters (Table 2). The increase in iron content first decreases the saturation magnetization (for x =0.2 at T= 10 K) then increases it again for x =OX The remanence, at the same temperature, follows the same vari- ation with x, but increases almost linearly with the saturation (Table 4).Elec trica I Behaviour The effect of temperature on the conductivity of the samples is directly observed by the plot of logo us. 1/T shown in Fig. 5. Semiconducting-type behaviour is observed [lo= ooexp(-E,/RT)] for all the compounds, and by extrapolation we obtain values of o for 773 K. The results of 0773 and the activation energies (E,) for all samples are presented in Table 5. The value of the conductivity for T= 773 K shows that the electrical conductivity decreases with increasing x.These results are consistent with the electronic structures of ruthenium and iron and their respective contents in the system studied. The Ru content decreases along the series, hence the 517 0 XO xu X 0 X X 0 X 0* * X 0 * X X 0 X X* * * * * * * ** -3 I I I 1.1 1.5 1.9 2.3 1O~WT Fig. 5 Variation of conductivity as a function of temperature for the system Co2Ru, -xFex04: x =(0)0.2; ( x) 0.5; ( ++ ) 0.8 Table 5 Electrical conductivity at 773 K and activation energy of the spinel system Co,Ru, -xFexO, 0.2 6.37 0.312 0.5 2.55 0.366 0.8 0.335 0.413 free-electron concentration decreases with the ruthenium con- tent, as was previously observed for the introduction of titanium in the system Co2Ru, -xTi,04.4 Conclusions From the results obtained we conclude that a solid solution is obtained for the system Co2Fe04-Co,Ru04. The samples prepared exhibit both semiconducting and ferrimagnetic behaviour. The authors acknowledge financial support from IN IC. References E. W. Gorter, Philips Rex Rep., 1954,9, 321. G. Blasse, Philips Res. Rep., 1964,3, 1. G. A. Sawatzky, F. Van Der Woude and A. H. Morrish, i'hys. Rec., 1969,187,747. B. Krutzsch and S. Kemmler-Sack, Muter. Res. Bull., 1984, 19, 1659. J. Dulac, Bull. Soc. Fr. Mineral Crystallogr., 1969,92,487. P. J. Murray and J. W. Linnett, J. Phys. Chem. Solids, 1976,37,619. R. D. Shannon and C. T. Prewitt, Acta Crystallogr., Secr. B, 1969, 925. J. C. Waerenborgh, PhD Thesis, University of Lisbon, 1993. Paper 3/04272C; Received 20th July, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940400515

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(4),519-523 Oriented Microporous Film of Tetramethylammonium Pillared Saponite Makoto Ogawa,*+ Masaru Takahashi, Chuzo Kato and Kazuyuki Kuroda* Department of Applied Chemistry, Waseda University Ohkubo-3, Shinjuku-ku, Tokyo 7 69, Japan Tetramethylammonium saponite film has been prepared and its structure has been characterized. By casting the aqueous suspension of the tetramethylammonium-saponite, a transparent film was obtained. The film is composed of oriented silicate particles with ab planes parallel to the substrate. The interlayer tetramethylammonium ions provide micropores in the interlayer space and the micropores are interconnected in the direction parallel to the silicate sheet. The film is regarded as a unique immobilizing medium for photoactive species because of the transparency and the anisotropic microporous structure.The study of photoprocesses of photoactive species within solids is a growing new field which yields a wide variety of useful applications such as sensitive optical media, reaction paths for controlled photochemical reactions, molecular devices for optics, etc.' For nanomaterials with ordered struc- ture the properties of the immobilized species can be discussed on the basis of the defined nanoscopic structures.2 Their structure-property relationships provide indispensable infor- mation for designing materials with novel chemical, physical and mechanical properties. Various states of surfactant assembly in solutions, inclusion compounds etc. have been in~estigated.~.~ Recently, zeolites have been utilized as a reaction vessel of molecular dimension^.^" Besides their stability compared to organic solids, zeolites possess many advantages for immobil- izing guest species.The confined size of the pore makes it possible to prepare and characterize metal and semiconductor clusters,&' and to obtain highly efficient charge separation in artificial photosynthetic systems.' The presence of intercon- nected micropores is useful for preparing conjugated polymers (so-called molecular wires)," and for aligning dipoles for second-harmonic generation." The processing of zeolites into films12 or larger crystals, and the preparation of the solids with different porous structure^,'^ are currently being investigated.Layered materials also act as stable immobilizing media with two-dimensional interlayer spaces. Among the possible layered materials, smectite is a group of 2 :1-type layered clay minerals consisting of negatively charged silicate layers (in which an octahedral sheet of aluminium or magnesium hydroxide is sandwiched by the tetrahedral silicate sheets) and readily exchangeable interlayer cations. It possesses vari- ous attractive features such as the swelling behaviour, ion- exchange properties, adsorptive properties and large surface area.I4,l5 The photoprocesses of photoactive species interca- lated in the two-dimensional interlayer space of smectites have been in~estigated.~,~,~,'~~~ Recently, in order to obtain more desirable conformation of guest species or to change the host-guest interactions, co-intercalation of organoammon- ium and organic polymer^^^,^^ have been reported.In our previous study on the photochemical hole-burning of quinizarin intercalated in ~aponite,~' we proposed the use of tetramethylammonium-saponite as a host matrix. From the hole-formation characteristics, the TMA-saponite was shown to be a versatile host matrix for optical and photochem- .I.Present Address: Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan. ical studies. In this paper, we report the preparation and the properties of a novel transparent film of tetramethyl-ammonium-saponite.Experimental Materials Synthetic sodium-saponite in powder form 100 mesh, Kunimine Industries Co., Japan; ideal formula Na1,3 [( Si,l,3Al,,3)(Mg3)Olo(OH)2]~nH20as thewas used starting material. Tetramethylammonium (abbreviated as TMA) chloride was purchased from Tokyo Kasei Industries and used without further purification. Anthracene (Wako Pure Chemical Industries Co.) and pyrene (Tokyo Kasei Ind. Co.) were used after recrystallization from benzene and etha- nol, respectively. N-salicylideneaniline (Wako Pure Chiemicals) was used as received. Sample Preparation The TMA-saponite was prepared according to the method described in the previous report.31 The TMA-saporzite was dispersed in deionized water and cast on a quartz or glass substrate to form a thin film.Intercalation of guest species into the TMA-saponite powder was carried out by stirring the TMA-saponite in the solutions of guest species. In order to incorporate guesi species into the film, the film and guest species (in powder) were placed in a closed vessel and allowed to react at devated temperatures (for example, 50 "C for the intercalation of N-salicylideneaniline) under reduced pressure. Characterization X-Ray powder diffraction was performed on a MAC Science MXP3 diffractometer with monochromatic Cu-Ka radiation. Infrared spectra of the KBr disks were recorded on a Perkin- Elmer FT-1640 Fourier-transform infrared spectrophoto-meter. DTA (differential thermal analysis) curves were recorded on a Shimadzu DT-30 instrument using a-alumina as the standard at a heating rate of 10°C min-l. Thermogravimetric analysis (TG) was performed on a Shimadzu TGA-40 instrument at a heating rate of 10 "C rnin-'.The adsorbed amount of TMA was determined by elemental analysis. UV-VIS absorption spectra were recorded on a Shimadzu UV-3lOOPC spectrometer. Luminescence spec- tra were recorded on a Shimadzu RF 5000 spectrophotometer. Transmission electron micrographs (TEM) were obtained on a JEOL JEM-1000CX transmission electron microscope oper- ated at 100kV. Nitrogen adsorption-desorption isotherms were collected at 77 K on a BELSORP 36 (BEL JAPAN Tnc.) after the samples were dehydrated at 150°C under vacuum for 5 h.Results and Discussion The X-ray powder diffraction pattern of the TOMA-saponiteis shown in Fig. l(a). The basal spacing is. 14.3 A, indicating an expansion of the interlayer space of 4.7 A, which is detejmined by subtracting the thickness of the silicate layer (9.6 A) from the observed basal spacing (14.3 A). The infrared spectrum of the product showed absorption bands characteristic of the tetramethylammonium ions. For instance, the C-N stretching vibration appeared at 1488cm-'. In the DTA curve of the product, an exothermic peak was observed above 300°C. Since the TG curve of the TMA-saponite showed weight loss around that temperature, the exothermic peak was ascribed to the oxidative decomposition of the TMA ions. All these results showed the formation of the TMA-saponite.From the elemental analysis of the product, the amount of the adsorbed TMA ion was 62 mequiv. per 100 g of clay (the cation exchange capacity of the saponite is 71 mequiv. per 100 g of clay), and only a trace amount of Na+ was detected in the product. Considering the change in the amount of adsorbed water and the formula weight, almost all interlayer exchangeable cations were thought to be substituted by TMA ions. It should be noted that the TMA-saponite still possesses swelling ability in water and can form transparent film on a quartz or Teflon substrate by casting the suspension. The X-ray diffraction pattern of the TMA-saponite film deposited on a glass substrate is shown in Fig. t(b). The diffraction pattern shows the basal spacing of 14.3 A, which is in agree-ment with that of the TMA-saponite powder.Since the d(001) diffraction peak is intensified compared with that of the powder and higher-order reflections have been observed, the film is thought to be composed of aggregated silicate particles with their ab planes parallel to the substrate. TEM obser-vations show the particles of saponite to be platelets with a radius of ca. 0.1 ym, which tend to aggregate. The TG curve showed that the film contained ca. 12 wt.% of adsorbed water, which should occupy both the interlayer micropore and the external surfaces. The hydrophilic nature of the surface as well as the small particle size and the tendency to aggregate is relevant to the film-forming ability.J. MATER. CHEM., 1994. VOL. 4 The transmission spectrum and the photograph of the film (the thickness is ca. 1.4 pm) are shown in Fig. 2 and Plate l(a), respectively. The film has no significant absorption in the wavelength range 250-2000 nm. Since the saponite used in this study does not contain iron, which is usually involved as inter-and intra-layer species of naturally occurring smectites, no colour due to iron oxides was observed for the TMA-saponite. This transparency is important for the appli-cation to optical and photochemical studies. If the TMA-saponite film was prepared on a Teflon plate, a self-supporting film was obtained. This film-forming ability is an advantage for practical applications. The surface of smectites is strongly hydrophilic owing to the surface oxygen layer and interlayer sodium ions.When *Or E c5 .-c E o~""'"''"'''~ 200 800 1400 2000 wavelengthhm Fig. 2 Transmission spectrum of the TMA-saponite film deposited on a quartz plate 1 I I I I I 1 5 10 15 20 25 30 35 40 28/degrees (Cu-Ka) Fig. 1 X-Ray diffraction patterns of (a) the TMA-saponite powder and (h)the TMA-saponite film Fig. 3 Schematic (b)side view structure of the TMA-saponite: (a) top view: J. MATER. CHEM., 1994, VOL. 4 the interlayer exchangeable cations are replaced by organo- ammonium ions, the surface properties change to become organophilic and the organoammonium-smectites do not swell in water.However, the TMA-saponite can swell in water to form transparent suspensions. This is probably due to the facts that TMA ions occupy only 15% of the hydrophilic surface of the silicate sheet even when all the interlayer exchangeable cations were replaced and that TMA ions are not so organophilic. Judging from the ideal surface area of TMA-saponite (ca. 690m2 g-o', which is calculated based on the surface area of 5.15 x 8.9 A for each cell)32 and the amount of the adsorbed TMA ions, the averag? distance between each pillar is deter- mined to be ca. 9.6A. Supposing that the TMA ion is a sphere with a radius of 2.5 A, we propose a! interconnected pore structure with a section of 4.6 x 4.7 A2 (Fig. 3). The calculated volFme of the interlayer spay (Vi) is determined as 1.6 x A3 g-' (345 m2 g-' x 4.7 A) and the volume (oVpillar)occupied by the adsorbed TMA ions is 2.4 x A3g-l, which is calculated from the adsorbed amount of TMA ions (0.62 mmol g-') of :he TMA-saponite and the volume of the TMA ion (ca.65 A3): Vpillar=65 x 0.62 x lop3x 6.02 x A3g-' =2.4 x A3 g-' The total pore volume Vporeis determined as 1.4 x A3 g-' by subtracting Gillarfrom Vi. Vpore = vi -%/pillar = 1.6 x 1023-2.4 x A3g-' = 1.4 x A3 8-l Based on the value and the ca&ulated volyme of the TMA-saponite (345 m2 g-' x 14.3 A =5.4 x A3 g-'), the porosity (volume YO)o{ the TMA-saponite is calculated to be ca. 26% (= 1.4 x A3 g-'/5.4 x A3 g-I). Note again that all the discussion about the micropores of the TMA-saponite has been made based on the supposition! that the TMA ion can be regarded as a sphere of radius 2.5 A and the pillars are distributed regularly in the interlayer space as shown in Fig.3. In order to calculate the surface area, the pilla! can be supposed to beo cylindrical with a base area of 20 A2 and a height of 4.7 A; we calculated the surface area of the TMA-saponite as for pillared clays. The available surface area of the silicate sheet is determined by subtracting the area (Apillar)occupied by the TMA ions from the calculated surface area (690 m2 g- ') of the TMA-saponite, where Apillar= 1.5 x A2 g-'= 150 m2 g-' From this, the area of the av!ilable silicate sheet is 540 m2 g-'. If the side of the pillar (74 A2 for each pillar; corresponds to 280m2 g-') is included, the total surface area would be 820 m2 g-'.Nitrogen adsorption-desorption isotherms for the TMA-saponite film are shown in Fig. 4. This adsorption largely follows a type I isotherm and shows microporosity for nitrogen with only a small macropore contribution, probably due to the external surfaces. This is consistent with the report by Yang and The porosity derived from the t-plot (0.182 cm3 g-') is almost consistent with the calculated value (0.14 cm3 g-'). The surface area of 316 m2 g-l, which is also obtained by a t-plot, is smaller than the value (540 m2 g-') calculated from the ideal structure. Considering the separation of the confronting silicate surfaces (0.47 nm) nitrogen can not cover both the surfaces completely.Because of the complicated geometrical structure of the TMA-saponite (Fig. 3), it is 200 r 0 0.2 0.4 0.6 0.8 1.0 PIPo Fig. 4 Nitrogen adsorption-desorption isotherm at 77 K: x =desorp-tion; 0 =adsorption difficult to assess the above-mentioned pore structure precisely by nitrogen adsorption-desorption isotherms. HON ever, the results obtained from the isotherms are compatible with the above-mentioned structure in which the TMA ions distribute homogeneously. The structure was also supported by the works on the properties of the TMA-smectites. 15333-35 This large surface area, as well as the high porosity men- tioned above, is a very attractive feature as an immobilizing medium for photoactive species.Being restricted by the silicate sheets, the pore is interconnected only in the direction parallel to the silicate sheets. Taking into account the structure of the TMA-saponite film, which is composed of oriented silicate particles with their ab planes parallel to the silicate sheets, the direction of the pore is parallel to the substrihte. This consistency of microscopic geometry with macroscopic is worth noting because the properties of the immobilized species can easily be discussed based on the structure and, as far as we know, no other porous materials have been reported to form such a geometry by such a simple process. A preliminary study on the adsorption properties of the TMA-saponite was carried out by using anthracene, pyrene and N-salicylideneaniline as guest species.The TMA- saponite powder was allowed to react with an ethanolic solution of pyrene or anthracene. When pyrene was used as a guest species (only a trace amount of pyrene was adsorked) the excimer-like fluorescence was observed in the emission spec- trum of the product even though the loaded amount of pyrene was very low. Note, when pyrene is forced into close proximity or is in high-concentration solution, excited-state dimers (excimers) are observed. Since the X-ray diffraction of the product shows !o change in the basal spacing (the interlayer spacipg of !.7 A) and the molecular size of pyrene is ca. 13.0 A x 7.2 A, there is no possibility of pyrene excimer forma- tion in the interlayer space.Therefore, it is considered that the observed excimer emission is due to pyrene adsorbed on the external surface of the TMA-saponite and that the accom- modation of pyrene molecules in the interlayer space is difficult. Fig. 5 shows the absorption and fluorescence spectra (the excitation wavelength is 320 nm) of anthracene adsorbed on TMA-saponite by reaction between the TMA-saponite powder and an ethanolic solution of anthracene. The spectra are similar to those obtained in solution and the wavelengths of the absorption and fluorescence maxima due to the 0-0 transition (380 and 384 nm for absorption and fluorescence, respectively) are close to those observed for the ethanol AB FL 400 500 wavelength/nm Fig. 5 Absorption and fluorescence spectra of the reaction product between the TMA-saponite and anthracene solution (375 and 377 nm, for absorption and fluorescence, respectively).This indicates that the adsorbed anthracene interacts rather weakly with the surface of the TMA-saponite. Since the adsorbed amount of anthracene is very low and the XRD pattern showed no change in the basal spacing, the possibility of the adsorption on the outer surface can not be excluded. A larger Stokes' shift should be observed for anthra- cene aggregated on the outer surface. In this case, the shift was small, indicating that the anthracene molecules are adsorbed molecularly between the pillars. The size of the micropore (Fig. 3) mentioned above in the TMA-saponite plays a major role in this guest selectivity.N-Salicylideneaniline . was introduced into the TMA-saponite film by a vapour-phase reaction. When the TMA-saponite film and N-salicylideneaniline powder are placed in a closed vessel in separated containers and the vessel is evacuated and heated (en. 50'C), the transparent film became yellow and the colour became deeper with prolonged reaction. [The photograph of the N-salicylideneaniline intercalated film is shown in Plate l(b).] The X-ray diffraction showed that the film was still orjented and the interlayer space expanded slightly by ca. 0.2 A. Thus, the vapour phase reaction is an applicable way to incorporate organic com- pounds into the TMA-saponite while retaining the oriented geometry of the TMA-saponite film.The absorption spectrum of the N-salicylideneaniline incor- porated in the TMA-saponite film showed absorption bands at cn. 350nm with vibrational structure and the spectrum is similar to that for a chloroform solution of N-salicylidene- aniline. Additionally, the prolonged reaction caused the Plate 1 Photographs of (u) the TMA-saponite film deposited on a quartz plate and (h) the film after the reaction with N-salicyl-ideneaniline J. MATER. CHEM.. 1994, VOL. 4 enol zwitterionic Scheme 1 Two possible configurations of N-salicylideneaniline increase in the absorbance, indicating the increase in the adsorbed amount of N-salicylideneaniline. N-Salicylideneaniline has been known to take two possible ground-state configurations (Scheme 1) depending on the environment, one is the enol form in non-hydrogen bonding solvents and the other is the zwitterionic form in hydrogen-bonding solvents.The observed absorption spectrum indicates that the intercalated N-salicylideneaniline takes the en01 form in the interlayer micropore. The absorption spectrum in combination with the absorption and fluorescence spectra of the anthracene adsorbed on the TMA-saponite showed that some organic compounds can be accommodated in the micro-pore of the TMA-saponite with weak interactions. This is consistent with the results of the hole formation of quinizarin incorporated in the TMA-~aponite.~' The adsorbed amounts of the guest species can be varied by changing the reaction conditions, i.e.reaction temperature and period. N-Salicylideneaniline was easily intercalated while it was difficult to incorporate anthracene and pyrene. The preparation of organoammonium-pillared saponites with different pillars, the detailed characterization of their adsorptive properties, and the applications of the pillared- saponites for photochemical hole burning, non-linear optics etc. are now underway in this laboratory and the results will be reported later. Conclusions The novel oriented transparent film of the tetramethylammon- ium-saponite has been prepared by casting the aqueous suspension. The interlayer tetramethylammonium ion pro- vides the interconnected micropore in the interlayer space and some ionically neutral organic molecules can be incorpor- ated into the micropore from vapour-phase or solution.The film is regarded as a unique anisotropic medium for immobiliz- ing photoactive species because the direction of the micropore is parallel to the substrate and the film is transparent in the 250-2000 nm wavelength range. The authors thank BEL JAPAN Inc., for the nitrogen adsorption-desorption measurements. The present work was partially supported by a Grant-in-Aid for Developmental Scientific Research from the Ministry of Education, Science and Culture and by The Sumitomo Foundation. References Photochemistry on Solid Surfaces, ed. M. Anpo and T. Matsuura, Studies in Surface Science and Catalysis 47, Elsevier, Amsterdam, 1989. Photochemistry in Organized & Construined Media, ed.V. Ramamurthy, VCH, New York, 1991. J. K. Thomas, Chem. Rev., 1993, 93, 301: J. K. Thomas, J. Phys. Chem. 1987,91,267. J. A. Ozin, Adv. Mater., 1992,4,612. G.D. Stucky, Prog. Inorg. Chem., 1992,40,99. S. L. Suib, Chem. Rev., 1993,93, 803. G. D. Stucky and J. E. MacDougall, Science, 1990,247,669. N. Herron, Y. Wang, M. Eddy, G. D. Stucky, D. E. Cox, K. Moller and T. Bein, J. Am. Chem. Soc., 1989, 111,530. 2. Li and T. E. Mallouk, J. Phys. Chem., 1987, 91, 643: Z. Li, J. MATER. CHEM., 1994, VOL. 4 523 C. M. Wung, L. Persaud and T. E. Mallouk, J. Phys. Chem., 1988, 92. 2592; M. Borja and P. K. Dutta, Nature (London), 1993, 21 H. Usami, K. Takagi and Y. Sawaki, J.Chem. Soc., Perkin Truns. 2, 1990, 1723. 10 11 12 13 14 15 16 17 18 19 362,43. P. Enzel and T. Bein, J. Phys. Chem., 1989, 93, 6270; P. Enzel, J. J. Zoller and T. Bein, J. Chem. Soc., Chem. Commun., 1992, 63; T. Bein and P. Enzel, Angew. Chem. Int. Ed. Engl., 1989,28, 1692; S. D. Cox and G. D. Stucky, J. Phys. Chem., 1991, 95, 710; S. Bordiga, G. Ricchiardi, G. Spoto, D. Scarano, L. Carnelli, A. Zecchina and C. 0.Arean, J. Chem. Soc., Faraday Trans., 1993, 89. 1843; C. Pereira, G. T. Kokotailo, and R. J. Gorte, J. Phys. Chem., 1991, 95, 705. S. D. Cox, T. E. Gier, G. D. Stucky and J. Bierlein, J. Am. Chem. SOC.,1988, 110, 2986; S. D. Cox, T. E. Gier and G. D. Stucky, Chem. Muter., 1990, 2, 609. T. Bein, K. Brown, P. Enzel and C. J. Brinker, Better Ceramics Through Chemistry Ill, Muter.Res. Soc. Symp. Proc., 1988, 121, 761. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature (London), 1992,359,710. The Chemistry of Clay-Organic Reactions, B. K. G. Theng, Adam Hilger, London, 1974. Zeolites and Clay Minerals as Sorbents and Molecular Sieves, R. M. Barrer, Academic Press, London, 1978. J. K. Thomas, Acc. Chem. Res., 1988,21,275. J. M. Adams and A. J. Gabbutt, J. Incl. Phenom., 1990,9,63. J. S. Yariv, A. Nassre and P. Bar-on, J. Chem. Soc., Faradaji Trans. 1, 1990,86, 1593 and references cited therein. T. Endo, T. Sato, and M. Shimada. J. Phys. Chem. Solids, 1986, 47, 799. 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Y. Okahata and A. Shimizu, Langmuir, 1989,5,954. T. Nakamura and J. K. Thomas, Langmuir, 1987,3,234.V. Kuykendall and J. K. Thomas, Langmuir, 1990,6, 1346; 1990, 6, 1350. T. Seki and K. Ichimura, Macromolecules, 1990,23,31. H. Tomioka and T. Itoh, J. Chem. Soc., Chem. Commun. 1991,532. K. Takagi, T. Kurematsu and Y. Sawaki, J. Chem. Soc., Perkin Trans. 2, 1991, 1517. M. Ogawa, K. Fujii, K. Kuroda and C. Kato, Muter Res. Soc. Symp. Proc., 1991, 233, 89; M. Ogawa, T. Aono, K. Kuroda and C. Kato, Langmuir, 1993,9, 1529. H. Miyata, Y. Sugahara, K. Kuroda and C. Kato, J. ('hem. Soc., Faraday Trans. 1,1987,83,1851. M. Ogawa, M. Inagaki, N. Kodama, K. Kuroda ant! C. Kato, Mol. Cryst. Liq. Cryst., 1992, 214, 141; M. Ogawa, M. Inagaki, N. Kodama, K. Kuroda and C. Kato, J. Phys. Chem. 1993, 97, 3819. M. Ogawa, T. Handa, K. Kuroda, C. Kato and T. Tarii, J. Phys. Chem., 1992,96,8116. An Introduction to Clay Colloid Chemistry, 2nd edn, H. Van Olphen, Wiley-Interscience, New York, 1977. Y. Yang and T. Bein, Chem. Mater., 1993,5,905. J.-F. Lee, M. M. Mortland, C. T. Chiou and S. A. Boycr, J. Chem. Soc., Faraday Trans. I, 1989,85,2953. J.-F. Lee, M. M. Mortland, C. T. Chiou, D. E. Kile and S. A. Boyd, Clays Clay Mineral., 1990,38, 113. 20 K. Takagi, H. Usami, H. Fukaya and Y. Sawaki, J. Chem. Soc., Chem. Commun., 1989,1174. Paper 31042745; Received 20th July, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940400519

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(4), 525-528 Ge-doped Bismuth Vanadate Solid Electrolytes: Synthesis, Phase Diagram and Electrical Properties Chnoong Kheng Lee: Meow Peng Tana and Anthony R. West*b a Department of Chemistry, Universiti Pertanian Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen, UK AB9 2UE The location of Ge-doped Bi4V20,, solid solutions in the Bi,0,-V,05-Ge0, ternary phase diagram has been determined; a more detailed study of the Bi4V20,,-Bi2Ge05 join has been carried out and the phase diagram presented. The main mechanisms for solid solution formation appear to involve substitution of both Ge and Bi into V sites, giving rise to the general formula Bi4+yV2-a2x-yGe2xOll -x-y: -0.04<y<0.23; O<x<O.45 (not all values of x and y in these ranges). Conductivity of the a and y polymorphs both on and off the Bi4V2OI1-Bi2GeO5 join generally decreases with increasing x after an initial increase.In addition, conductivity of the y polymorph decreases with increasing Bi,O, content, y; the highest conductivity was obtained at x =0.305 and y =0.07. .,met astable Solid solutions based on Bi,V20,, are a new family of oxide ion conductors.' DTA and X-ray studies have confirmed the existence of three polymorphs: c1 (orthorhombic), p and y (both tetragonal). The bismuth :vanadium ratio is variable, with YOBi203 ranging from 66.67 to 70.40., For most of the solid solution compositions, it is not possible to quench the high-temperature y polymorph to room temperature; trans- formation to a always occurs.' With increasing Bi,03 content, however, it is possible to quench first the p and then the y polymorph to room temperature, where these phases are The structures proposed for the different polymorphs can all be described in terms of alternating Bi,O;+ sheets and perovskite-like V03.' 0i.; layers. Full structural detemi- nation has not been possible owing to twinning,' the occur- rence of an incommensurate supercell, disorder of both oxygens and cations3 and the presence of a supercell (3-fold along a and/or b).,Disorder in the oxide ion vacancies in the perovskite-like layers is supposedly responsible for the high anionic conductivity observed in the y p~lymorph.~ A new family of anionic conductors, BIMEVOX, was derived by partial substitution of vanadium by other metallic ions such as Cu and Ni.These substitutions prevent ordering of the metallic positions and/or oxygen vacancies, and allow the highly conductive y polymorph to be stabilized to room temperat~re.~Oxygen transport number measurements indi- cated that 0'-ions were the main charge carriers.' Substitution of various elements, M, for vanadium in the Bi,V,O1 structure has been studied;"* electrical measure- ments showed that the nature and concentration of the sub- stituent had some effect on the conductivity; these substitutions enabled the tetragonal y phase to be preserved to room tem- perature. The highest conductivity reported so far is that of Bi2V0.9Cu0.105,35,with 0value of 3 x R-cm-' at 300 "C.All of the previous studies have concentrated on introducing dopants into stoichiometric Bi4V2Ol1 by the replacement V+M. In this study, a survey of the doping of Bi4V2011 solid solutions by Ge was carried out by reference to the ternary phase diagram Bi203-V,O,-Ge02. From the locus of the solid solutions, it was possible to estimate the doping mechan- ism; a more detailed study of the 'stoichiometric' join: Bi,V,O, ,-Bi,GeO, was carried out. Conductivity of selected c1 and y phases has been measured as a function of temperature. Experimental Ge-doped bismuth vanadate solid solutions were prepared by solid-state reaction in gold foil boats at 850-880°C in air.Starting materials were 99.9% Bi2o3, 99.9% V205 and 99.99% GeO,. Phase purity of the samples was determined using a Philips X-ray diffractometer, Cu-Ka, radiation. Weight-loss checks on selected samples showed that material loss through volatilisation was not significant. Hence the overall product stoichiometries were the same as those of the starting materials. For the phase diagram determination, the samples were air- quenched after heating at various temperatures for 2 h. Melting temperatures were determined approximately from the appearance of pelleted samples after heating isothermally in 5 "C steps. Owing to the corrosive nature of Bi-containing melts towards Pt, it was decided not to use DTA to try to obtain more accurate determination of melting temperatures. Although the absolute melting temperatures determined from the appearance of pellets may not be very accurate, the nature of their variation with composition could be determined readily.Phase transition temperatures were determined by DTA in N2 with a Du Pont 991 instrument, with heating and cooling rates of 10"C min- '. Pellets for electrical property measurements were cold-pressed, sintered at 850-880 "C overnight and Au paste elec- trodes were fired on at 200-600°C. AC impedance measure- ments were made over the range 25-800°C using a Hewlett- Packard 4192A impedance analyser using the frequency range 10- 106 Hz. Samples were equilibrated at constant temperature for 30min prior to each set of measurements.All mleasure- ments were made in air; previous measurements' on phase materials showed that the conductivity values did not change in different measuring atmospheres: Ar or 0,. Results and Discussion Phase Diagram An investigation into the compositional extent of Ge-doped Bi,V,O,, showed that an extensive area of solid solutions was obtained in the +(Bi203)+( V205)-Ge0, phase diagram. The +(Bi203) content ranged from ca. 65.8 to ca. 70.2% and the maximum GeO, content was 15.5%, Fig. 1 (top). For +(Bi203) content <65.8%, a small amount of BiVO, was present as a second phase; with >15.5% Ge02, the additional phase appeared to be Bi,(Ge04)3. Within the Bi,V20,, solid solution area and at low BiZ03 content, only the a phase was obtained at room temperature irrespective of cooling rate; at higher Bi203 content, however, monophasic samples of all three polymorphs, a, p and y, were formed, depending on both composition and cooling rate.The results shown in I /O t a--y4 ... f/" Fig. 1 Top: location of the Bi,V,O,, solid solutions in the Bi20,-Ge02-V20, ternary system. 0,Single-phase and 0,multi-phase samples; as shown by X-ray powder diffraction, for samples that were cooled in air after reaction at 850-900°C. Solid solution limits on the Bi,O,-V,O, edge are taken from ref. 2. Bottom: composi- tion range of the Bi4+yV2-2x-yGezxOll -x-y solid solutions. 0,single-phase and, 0, multiphase samples, as shown by X-ray powder diffraction Fig.1 are for samples that were removed from the furnace at the end of the heating cycle and allowed to cool naturally in air. The solid solutions appear to run parallel to the Bi,V,O,,-Bi,GeO, join, Fig. 1 (a), indicating that the main mechanism involves substitution of Ge into V sites, together with oxygen vacancy creation, as represented by the formula, Bi,V, -2xGe2x01 The varying Bi :V ratio at constant x-X. suggests the additional possible mechanism: Vs+ +0,-+ Bi3+, giving rise to the formula Bi4+yVZ-yOll-y; this also entails oxygen vacancy creation. The overall general formula for the ternary solid solutions may therefore be written as Bi, +,,V2-2x -,,GezxOll--,,. The single-phase region can be described in terms of a compositional grid with axes rep- resenting Bi +V exchange (horizontal axis) and V +Ge exchange, as shown in Fig.1(bottom). The solid solutions are most extensive in the x direction, which indicates V5+ $ Ge4+ substitution to be the main doping mechanism. This is not surprising as Ge4+ and V5+are very similar in their ionic size. However, the solid solution is most extensive off the stoichiometric join with a limit at yzO.1, xxO.45. Partial substitution of V5+ by Bi3+, which is a significantly larger ion, has probably distorted the structure in such a way as to J. MATER. CHEM., 1994, VOL. 4 facilitate further substitution of V5+by Ge4+. Decailed crystal- lographic study is required to confirm the locations of the various atoms and hence the substitution mechanism.A partial phase diagram of the join Bi,V,O,~-Bi,GeO, is shown in Fig. 2. Solid solutions form of general formula Bi,V,-2xGe2x011-x: 0 <x<(0.225-0.30), the limit depending on temperature. Melting temperatures show a gradual increase with x. The a+P-+y transition temperatures were determined by DTA; data shown in Fig. 2 were obtained on the heating cycle. The transitions were usually reversible on the cooling cycle of DTA but showed significant broadening and hysteresis on cooling with increasing dopant content, particularly for the fl+a transition. For the entire single-phase region, O<x<O.35, it was not possible to quench the 7 polymorph to room temperature; transformation to a always occurred. Stabilization of the high-temperature y polymorph to room temperature has been reported for Bi,V,Oll doped with Cu, Ni, C0~9'3~ and other divalent, tetravalent and pentavalent In the present study, however, stabilisation of the y phase was observed only for compositions off the 'stoichio- metric' join, Fig. l(a).The formation of a complete solid-solution series on the Bi,V,O1 ,-Bi,GeO, join was reported by Koshelyaeva et a/.' Single crystals were isolated from melts with different starting compositions. Crystals with 0.45 <x <0.5 in the formula Bi,(Gel -xVx)2011+ were tetragonal while the other composi- tions were orthorhombic. In the present study, by contrast, we were not able to obtain the complete solid-solution series. The lattice parameters of the a polymorph as a function of Ge content are shown in Fig.3; c increases with increasing Ge content whereas a, h and the cell volume decrease. Introduction of Ge, which is of similar size to V but of lower charge, may result in an increasing number of oxygen vacanc- ies and a slight decrease in cell volume. Conductivities Conductivity values were obtained from complex impedance plots. At low temperatures, e.g. 200°C and on the heating cycle [Fig. 4(a)] two overlapping arcs were seen with associ- ated capacitance (after correction for blank jig capacitance) of typically 6.5 x lop1, F cm-I and 3.1 x lo-"' F cm-'; these are attributed to bulk and grain-boundary regions, respect- ively. As temperature increased, an additional low-frequency spike became increasingly prominent.At e.g.400 'C [Fig. 4(b)] 0 00 0 Bi4V2OI1 0.15 0.30 0.45 0.60 0.75 x in Bi,V2 -2fie2Jl,1 --Bi,Ge05 Fig. 2 Partial phase diagram of the Bi,V20, ,-Bi2Ge0, join. 0,melting temperatures of pellets; x , DTA transition temperatures on heating; widths of (a+B) and (/I+?) two-phase regions are schematic only; 0, Single-phase and, 0,multiphase samples, as shown by X-ray powder diffraction J. MATER. CHEM., 1994, VOL. 4 t t x in Bi4V2 -,fie2f11 1 - Fig. 3 Variation of cell parameters with Ge content 42( 28( 14( 1o3 lo2, 0" O0 0 0 oooo O O O0 O.oOOBoo~o*o RT I I I J $ ?-h 140 280 420 560 9.6 10 0 0 7.2 0 0 4.8 0 0 0 0 2.4 - the spike is well developed and inclined at ca.60' to the horizontal; it has an associated capacitance of typically 1.6x F cm-'. This effect is characteristic of ionic polariz- ation phenomena at the blocking gold electrodes and supports the idea that conduction is ionic. As in the case of Bi4V20,, solid solutions2 and other doped Bi4V201 phases;','-' there-fore, the main conducting species in the y phase appears to be oxide ions: dc polarization measurements2 indic%ated that conduction was predominantly by oxide ions. In the low- temperature a phase, there may be a significant amount of either electronic or protonic conduction.2 The general shapes of the Arrhenius plots of the Ge-doped Bi,V2011 solid solutions are similar to those of the undoped system and have similar activation energies.2 Conductivity isotherms of the solid solutions on the 'stoichiometrtc' join as a function of dopant concentration are shown in Fig.5. Data at 300, 400, 600, 650°C are for a,%,y,y polymorphs, respect- ively. There appears to be an increase in conductivity with initial doping at all temperatures, after which a sligh! decrease occurs. The conductivities were reversible through rhe fl and 7 regions on the heat-cool cycle, but on cooling through the p to a region the conductivities showed significant hysteresis. Similar phenomena were observed in undoped material2 and in Cu-doped Bi4V2OI1, although the reason for the lack of reversibility of the a +fl transition remains unclear. ' Conductivity isotherms of Ge-doped y phases with varying Bi20, content, y, at constant x are shown in Fig. 0.At x= 0.25, conductivity values were similar for compositkons with y=O.O7 and 0.11 but decreased at higher y values. The data shown in Fig. 6 all correspond to the y polymorph. At y=O.O7 and with varying x, the highest conductivity was observed for a sample with x=0.305, corresponding to the formula Bi,~,,V,,32Geo.61010.625at temperatures below 450 "C; at higher temperatures, however, conductivity gener- ally decreased with increasing Ge content (Fig. 7 1. In the Ge-doped solid solutions studied, the highest conductivity &A A 400C 0.075 0.150 0.225 0300 x in Bi4V2 -2fie2f11 -Fig. 5 Isothermal conductivity as a function of Ge content for compositions on the Bi,V,O,,-Bi,GeO, join.H, heating cycle; C, cooling cycle J. MATER. CHEM., 1994, VOL. 4 & observed at 300°C is 1.2 x R-' cm-', one order of -1 -magnitude lower than the highest value reported for Cu- and Ni-doped material.3 -2 -Conclusions i550 Systematic doping of Bi4V2011 solid solutions with Ge -3--6-,-0.08 0.14 0.20 0.26 Y in Bi4+yV2-2x-fie2flll -x-y Fig. 6 Conductivity isotherms ("C) for Bi4+yV2-2x-yGe2x011 -x-y solid solutions at x =0.25 \\ -6 0.255 0.315 0.375 resulted in the formation of an extensive area of solid solutions; monophasic regions of a, p and y polymorphs form depending on composition. The main solid-solution mechanism appears to involve substitution of Ge into V sites, as the principal direction of the solid solutions in the phase diagram is parallel to the Bi4V2011-Bi2Ge05 join.The conductivity behaviour of the doped y phases is similar to that of the undoped system; conduction is mainly by oxide ions. Highest conductivity was observed for a doped y phase with x=0.305 and y=O.O7, i.e. Bi4,0,Vl~,2Geo~~10~o~~~~;however, its conductivity is one order of magnitude lower than that of the best Cu- and Ni-containing BIMEVOX conductors. C.K.L. is grateful to the Majlis Penyelidikan Kemajuan Sains Negara, Malaysia for financial support (Grant No. 2-07-05-009) and to Mr. Azali Md. Sab, Soil Science Dept., UPM, for assistance with the XRD analyses. References F. Abraham, M. F. Debreuille-Gresse, G. Mairesse and G. Nowogrocki, Solid State Zonics, 1988,28-30, 529. C. K. Lee, D. C. Sinclair and A. R. West, Solid State Zonics, 1993, 62,193. F. Abraham, J. C. Bovin, G. Mairesse and G. Nowogrocki, Solid State Ionics, 1990,40-41,934. K. B. R. Varma, G. N. Subbanna, T. N. Guru Row and C. N. R. Rao, J. Mater. Res., 1990,5,2718. T. Iharada, A. Hammouche, J. Fouletier and K. Kleitz, Solid State Ionics, 1991,48,257. R. Essalim, B. Tanouti, J. P. Bonnet and J. M. Reau. Muter. Lett., 1992, 13,382. J. B. Goodenough, A. Manthiram, M. Paranthaman and Y. S. Zhen, Mater. Sci. Eng., 1992, B12, 357. J. C. Bovin, R. N. Vannier, G. Mairesse, F. Abraham and G. Nowogrocki, ISSZ Lett., 1992,3, 14. V. G. Koshelyaeva, A. A. Bush, Yu. V. Titov and Yu. N. Venevtsev, Russ. J. Inorg. Chem., 1988,33, 1815. Paper 3/04317G; Received 21st July, 1993 Fig. 7 Conductivity isotherms ("C) for Bi,+,V2-2x-yGe2xOll-x-y solid solutions at y =0.07

ISSN:0959-9428    

DOI:10.1039/JM9940400525

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(4), 529-532 Preparation and Characterization of Heavy-metal Oxide Glasses: Bi,O,-PbO-B,O,-GeO, System Victor C. Solano Reynosot Luiz C. Barbosa: Oswaldo L. AIves,b Norbert0 Aranhaa and Carlos L. Cesara a lnstituto de Fisica Gleb Wataghin, UNICAMP, P.O. Box 6165, Campinas, SP, 13081, Brazil Laboratorio de Quimica do Estado Solido, lnstituto de Quimica, UNICAMP, P.O. Box 6154, Campinas, SP, 13081, Brazil High-refractive-index glasses of heavy-metal oxides have large optical non-linearities which make them promising for optoelectronic applications. This paper describes the fabrication and characterization of the xBi203-Pb0-B203-(52 -x)Ge02 (BPBG) glass system with x =10, 15, 20, 30 and 35.The BPBG glasses were melted in a high-purity alumina crucible placed in a Super Khantal resistance furnace at 1000 "C for 30 min and then poured onto a steel plate.The characterization was done by X-ray diffraction (XRD), density, dilatometry, light absorption (UV-VIS-IR) and linear refractive-index measurements. The infrared spectra show the presence of BiO, and GeO, in the glass structure suggesting a network former role for the bismuth oxide. These measurements allowed us to estimate the non-linear refractive index n2, using Line's formula, to be as high as 1.5 x 10-l8m2W-'. The recent interest in high-refractive-index glass systems is due to their large optical non-linearities. This property can be enhanced further by the presence of heavy-metal oxides, such as Bi203 and PbO, in the glass structure, making these heavy-metal oxide glasses promising for optoelectronics appli- cations, non-linear optics' and other applications based on high refractive index.2 Furthermore, these glasses show acou- sto-optical and magneto-optical proper tie^.^ The chemical and physical properties of the glasses are intimately related to their structure^.^ This work describes the preparation of the quaternary system Bi,0,-PbO-B,03-Ge02 (BPBG) glasses and their characterization using X-ray diffraction (XRD), density, dila- tometry, light absorption (UV-VIS-IR) and linear refractive- index measurements. Experimental The compositions of the BPBG glasses used in this study are listed in Table 1.Batches of ca. 50 g of glass have been prepared by mixing reagent-grade bismuth(u1) oxide, lead@) oxide (both from Riedel j, boric acid (Merck) and extra pure germanium dioxide (Kawecki Berylco).This mixture was melted in a high-purity alumina crucible placed in a Super Khantal electrical resistance furnace at 1000"C for 30 min and then poured onto a cold stainless-steel plate, followed by 5 h annealing at 350°C. We made samples in three forms: 0.5mm thickness slabs for the UV-VIS-IR, powder for the XRD and IR, and blow thin films for absorption-coefficient measurements. The XRD patterns were obtained with a Model 3X-A Shimadzu diffractometer with an Ni filter using Cu-Ka radiation (1.5418A). Infrared spectra were recorded in the 4000-400cm-' region for the slabs or KBr pellets on a Nicolet 60SX-B Fourier transform spectrometer.Absorption Table 1 BPBG glass system compositions (mol%) glass ~~~~~ Bi,03 PbO B203 GeO, BPBG-1 10 40 8 42 BPBG-2 15 40 8 37 BPBG-3 20 40 8 32 BPBG-4 30 40 8 22 BPBG-5 35 40 8 17 spectra (200-900 nm) were obtained on a Cary-Varian 2300 spectrophotometer. Density measurements were carried out on Micromeritics Multivolume Pycnometer model 1305 using helium as the displacement gas. The thermal dilatation data were obtained with a Harrop dilatometer. The linear refractive index was measured by the Brewster angle method at 632.8 nm with an He-Ne laser. Results and Discussion Glass Formation Using the procedure described in the Experimental we obtained bubble-free transparent glasses with a yellou colour- ation and high homogeneity.All the compositions showed the typical halo (28=28"j in the XRD patterns, indicating that the samples are amorphous. There was no sign of crystallization even for the compositions containing 3 5 mol% of Bi203 and 40 mol% of PbO. This result confirms Beck and Taylor's idea about the minimum bismuth and lead oxide concentrations to the stability of the amorphous phase.' Density Fig. 1shows the density dependence on the glass compositions. The density value increases with the Bi,03 concentration. The substitution of the GeO, by the heavier Bi203 oxide could explain this behaviour. However, the bonds with Bi,03 are more covalent than the bonds with GeO,, which tends to increase the density also.The density tends to saturate for the higher Bi203 concentrations (BPBG-4 and BPBG-5 samples). The weight of Bi203 compared to GeO, and the increase in the covalent bond character can explain only the increase in the density and not the saturation. The only mechanism which can oppose continuous density enhancement is the increase in the Bi-0 bond distance. It seems that this increase in the Bi-0 bond distance happens after the 25 mol% Bi2O3 con- centration. A hypothesis for this is that initially the Bi203 stands in an interstitial site of the glass network. As these sites saturate, Bi203 is forced to a substitutional site where the Bi-0 bond distance is affected. This picture is coherent with the estimates for the non-linear index n2 discussed later.The BPBG densities are small compared to other bismuth and lead glass systems.6 530 6.8 -7 6.6-5ln \-x .-c u)C4 6.4-10 15 20 25 30 35 Bi203(mol %) Fig. 1 Effect of Bi,03 content (mol%) on the density of the Bi,O,-PbO-B,O,-GeO, glass system (see Table 1) Dilatometry Fig. 2 shows the thermal expansion coefficient, in the (130-160) x lop7 K-' range, as a function of the Bi20, con- centration. Similar orders of magnitude have been reported in the literature for other quaternary heavy-metal oxide gla~ses.~The thermal expansion coefficient shows small vari- ations with the Bi,03 concentration, but the glass-transition temperature (T,) and the softening point temperature (Td)are very sensitive to the Bi,O, concentrations, as shown in Fig.3. The decrease in Tgusually means a more open glass network, while the increase in the thermal expansion coefficient usually means weaker bonds. The difference between Td and the T,, for the whole composition range, is roughly constant, as shown by Fig. 3. Linear Refractive Index We expected a high refractive index for these heavy-metal oxide glasses due to the large Bi and Pb p~larizability'~~ and, indeed, Fig. 4 shows a 1.93-2.20 BPBG refractive index n. The increase of refractive index with Bi203 content (Fig. 4) was also observed by other authors for similar systems." Canale et studying the binary system Bi,O,-GeO, and PbO-GeO,, attributed this change to the lead or bismuth oxides region on the glass network.On the other hand, it is well known that Ge02 or PbO tends to increase the refractive index, making it hard to understand the role of the Bi203 on this index. -1601 J. MATER. CHEM., 1994, VOL. 4 10 15 20 25 30 35 Bi203(mol %) Fig. 3 Effect of Bi203 content (mol%) on the T, (0)and Td (B) temperatures of the Bi,0,-Pb0-B20,-Ge0, glass system (see Table 1) 2.5 I ---I 1.5 10 15 20 25 30 35 Bi203(mol Yo) Fig.4 Linear refractive index uersus Bi,O, content (mol%) of the Bi,O3-Pb0-B2O3-GeO, glass system (see Table 1 ) Spectral Characteristics U V-VIS Spectra Fig. 5 shows the effect of the Bi,O, content on the UV-VTS cut-off for BPBG glasses. We assign the cut-off value for the wavelength where the extrapolation of the decay in trans- mission curve in the UV region reaches the zero transmission. The red shift in the cut-off with the Bi,03 concentration was also observed for other heavy-metal glasses, for example, lead 100 I10 15 20 25 30 35 10 15 20 25 30 35 Bi203(mol %) Bj2O3(mol Yo) Fig.2 Effect of Bi,O, content (mol%) on the thermal expansion Fig. 5 Effect of Bi203 content (mol%) on the ultraviolet cut-off coefficient of the Bi,O,-PbO-B,O,-GeO, glass (see Table 1) wavelength of the Bi,O,-PbO-B,O,-GeO, glass system J. MATER. CHEM., 1994, VOL. 4 gallobismuthates.' The electronic transitions from the valence to the conduction bands are in the range 0.35-0.45 pm, depending on the glass composition.The absorption coefficient cx was measured using the thin blown glass film samples. Fig. 6 shows the plot of J(rE) us. E, where E is the photon energy in eV. We determined the optical gap Eoptas the energy where the extrapolation of J(zE) crosses the JcxE=O axis (Fig. 7). The Urbach tail AE was obtained from the slope of the In a us. E in the UV region. There is clearly a red shift with the Bi203 concentration as shown in Fig. 6 and 7. According to Lines'' the Sellmeier gap (E,) is given by E, 5 2(Eopt+AE),and it can be fed into his formula, n2= { 3.4(n2+2)(n-l)d2/(nEz)}x lo-,' m2 W-', to estimate the non-linear refractive index (n,). The parameter d is tbe metal -oxygen bond distance and was estimated as 2.3-2.5 A. Fig. 8 shows these estimates as a function of Bi,O, concentration.The values are in the range (60-150) x m2 W-', 20-50 times larger than the nz in silica, and agree with published results for other heavy-metal oxide glasses.12 There are two regions of non-linear index n,: a low value region, -IN 'G -IN .2-1% UI 8 Y {j //I/// I/0 I 2.50 2.75 3.00 3.25 3.50 energytev Fig. 6 ,'YE versus E plot for xBi203-40Pb0-8B,03-( 52 -x)GeO,. (a) u=10; (b)x=15; (c) x=20; (d) x=30 and (e) x=35 3.1 2.9 2.8 i Fig.7 Optical gap Eopt uersus Bi203 content (mol%) for the Bi,0,-PbO-B,0,-Ge02 glass system 531 -140 7 120-3 c\I E 0Y 100-z--..c" c8ol60 10 15 20 25 30 35 Bi203(mol "A) Fig. 8 Estimated values of non-linear refractive index as fiinction of Bi,O, content (mol%) of the Bi,O,-PbO-B,O,-GeO, glass (see text) (60-80) x m2W-' for a Bi203 content of 10-20mol% and a high value region, (140-15O)x 10-20m2 W -'for a Bi203 content of 30-35 mol%.The change in refractive index from 1.93 to 2.2 increases the n2 by 34%, and the change in the Sellmeier gap is responsible for another 32% increase. The remainder (19Y0) comes from changes in ihe bis-muth-oxygen bond distance, d, which has increased This is consistent with the density saturation for high Bi203 content. Infrared Spectra The BPBG glasses infrared spectra in the regioiz 1400-400 cm-' are presented in Fig. 9. The strong broad band with a minimum at 750 cm-' for the BPBG-1 sample, can be attributed to the Ge-0-Ge stretching mode.13 The other broad band observed for all compositions, situated in the range 1350-1100 cm-', are related to B203 vibration^.'^ The behaviour with the Bi203 content has three main features: (i) the broad band assigned to Ge-0-Ge stretching mode shows a shift from 750 to 700 cm-l and a smaller baridwidth; (ii) the shoulder at 800 cm-' appears as a defined we<tk band at 860 cm-'; (iii) the band at 550 cm-I practically disappears and another one with a minimum near 450 cm-l is observed, see Fig.9 insert. The band at 750cm-' is shifted to lower wavenumber in this glass family when compared to the pure GeO I (tetra-hedral) band minimum at 890 cm-'. This shift h<is been interpreted as due to the appearance of non-bridging <)xygens (depolymerization) in the germanium oxide network13 and the consequent change in the germanium coordination frc )m four (tetrahedral) to six (octahedral).The fact that there is a minimum at 750 cm-' even for the Bi203 poorest com~sosition suggests the presence of GeO, octahedra in this glass system. The small changes from 700 to 750cm-' indicate that the Pb2+ (constant at 40 mol%) already made the depol ymeriz- ation of GeO, network which makes the Bi3+ conti ibution to the formation of this non-bridging oxygen insignificant. The weak band observed at 860cm-' has been assigned to the distorted Bi06 octahedra, and has been taken as a sign of the network forming role of bismuth oxide.15.16 Finally, some comments about the 450 cm-' band.This band has been assigned to 0-Ge-0 and frequently ,ippears in GeO, g1a~ses.l~The disappearance, or shift tc lower wavenumbers, of the 450cm-' band for the bismuth-rich wavenumberlcm-’ I,,I*I*I,IIlIII I 1 1 1400 1200 1000 800 600 400 wavenurnber/cm-’ Fig. 9 IR spectra (1400-4OO cm-’) of xBi203-40PbO-8B203-(52-x)Ge02. (a) x =10; (b)x = 15; (c)x =20; (d) x =30 and (e)x =35. Inset shows 450 cm-’ band region. composition can be explained by the decrease in the GeO, content, which would explain the disappearance, and/or by a vibrational coupling involving the Bi- 0 stretching and defor- mation vibrations of the germanium oxide networks, which would explain the shift to lower wavenumbers.17 A similar effect was observed in the binary system Bi2O,-Ge0,.l3 Conclusions The Bi,03-PbO-B,O,-GeO, system forms glasses with great homogeneity and stability.Thermal expansion coefficient, J. MATER. CHEM.. 1994, VOL. 4 density, linear refractive index and UV-VIS spectra are depen- dent on the Bi,O, content. The estimated value of non-linear refractive index, as high as 150 x lo-,’ m2 W-l. suggests the potential use of these glasses in optoelectronic applications. Infrared spectra show features that can be interpreted as due to the network-forming role of bismuth oxide and the presence of Ge06 groups. At the moment, systematic studies for other glass compositions, Raman and non-linear properties measurements are in progress in our laboratory.The authors acknowledge the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq),Fundaqiio de Amparo a Pesquisa do Estado de Siio Paulo (FAPESP), Programa de Apoio ao Desenvolvimento Cientifico e Tecnologico (PADCT) and the Telecomunica@es Brasileiras S/A (Telebras) for financial support. References 1 D. W. Hall, M. A. Newhouse, N. F. Borelli, W. H. Dumbaugh and D. L. Weidman. Appl. Phj’s. Lett., 1989,54, 1293 2 0. H. El-Bayoumi, A. A. Said, R. J. Andrews, hl. J. Suscanage, T. P. Swiller, J. H. Simmons and Van Styland, Bol. Soc. Esp. Ceram. Vid., 1992,31,3-c, 9. 3 J. C. Lapp, H. Dumbaugh and M. L. Powley, Rit.. Sftaz. Sper. Vetro, 1989, 1,91. 4 J. E. Canale, R. A. Condrate, Sr., K. Nassau and B. C. Cornilsen, J. Can. Ceram. Soc., 1986,55, 50. 5 W. R. Beck and N. W. Taylor, USPut 2853393, 23 September, 1958. 6 J. A. Ruller and J. E. Shelby, Phys. Chem. Glass., 1992,33, 177 7 H. J. L. Trap and J. M. Steves, Phjs. Chem. Glass., 1960,1, 181. 8 J. E. Shelby, J. Am. Cerum. Soc., 1988,71, C254. 9 W. H. Dumbaugh, Phys. Chem. Glass., 1986,27,119. 10 J. A. Ruller and J. E. Shelby, Phys. Chem. Glass., 1992,33, 177. 11 M. E. Lines, J.Appl. Phys., 1991,69,6876. 12 H. Nasu and J. D. Mackenzie, Opt. Eng., 1987,26,102. 13 J. E. Canale, R. A. Condrate, K. Nassau and B. C. Cornilsen, Muter. Res. Symp. Proc., 1987,89, 169. 14 J. Wong and C. A. Angel, Gluss: Structure by Spectroscopy, Marcel Dekker, New York, 1976. 15 F. Miyag, T. Yoko and Sakka, J. Non-Cryst. Solids, 1990, 126, 170. 16 A. Bishay and C. Maghrabi, Phys. Chem. Gluss., 1969,10,1. 17 S. C. Abrahams, P. B. Jamieson and J. L. Berstein, J. Chem. Phys., 1967,47,4034. PaDer 3104346K: Received 2 1st Julj?, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940400529

出版商:RSC    

年代:1994

数据来源: RSC