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Front cover |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 017-018
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ISSN:0959-9428
DOI:10.1039/JM99404FX017
出版商:RSC
年代:1994
数据来源: RSC
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Back cover |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 019-020
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ISSN:0959-9428
DOI:10.1039/JM99404BX019
出版商:RSC
年代:1994
数据来源: RSC
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Contents pages |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 041-042
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摘要:
ISSN 0959-9428 JMACEP(5) 653-779 (1994) Journal of Materials Chemistry Synthesis, structures, properties and applications of materials, particularly those associated with advanced technology CONTENTS 653 High-temperature thermoelectric properties of Inz03-based mixed oxides and their applicability to thermoelectric power generation M. Ohtaki, D. Ogura, K. Eguchi and H. Arai 657 Syntheses of soluble polymeric Lewis bases and their adducts with metal alkyls X. Li, C. M. Lindall, D. F. Foster and D. J. Cole-Hamilton 663 Preparation of an Na3Zr,Si,P01,-sodium aluminosilicate composite and its application as a solid-state electrochemical CO, gas sensor S. Nakayama and Y. Sadaoka 669 Influence of methane on the nitriding gas reduction of kaolinite A. Seron, J.Thebault and F. Beguin 675 Electroluminescence of organic thin films based on blends of polystyrene and fluorescent dyes P. Frederiksen, T. Hjernholm, H. G. Madsen and K. Bechgaard 679 1,3-Disubstituted ferrocene-containing thennotropic liquid crystals of form (q5-C5H5)Fe [(q5-C5H3)-1, 3-(C0zC6H4C02C6H40('nH2n+ 1)2] R. Deschenaux,J. Santiago, D. Guillon and B. Heinrich 683 Studies of vapour-phase chemical derivatisation for XPS analysis using model polymers I. Sutherland, E. Sheng, D. M.Brewis and R. J. Heath 689 Vapour-phase synthesis of titanium nitride powder J. P. Dekker, P. J. van der Put, H. J. Veringa and J. Schoonman 69 5 Co-pyrolysis of hydrocarbons and SiEt, for the synthesis of graduated Si,C1-, ceramic thin films by chemical vapour deposition J.M. Agullo, F. Fau-Canillac and F. Maury 703 Bi2Wl-,Cu,06-, (0.7GxG0.8): A new oxide-ion conductor V. Sharma, A. K. Shukla and J. Gopalakrishnan 707 Crystal structures of two sodium yttrium molybdates: NaY(MoO,), and Na,Y(MoO,), N. J. Stedman, A. K. Cheetham and P. D. Battle 713 Electret behaviour of di- and tri-nuclear iron hydrazone-hexacyanoferrate compounds studied by the thermally stimulated depolariz- ation current technique A. Bonardi, R. Capelletti, C. Pelizzi and P. Tarasconi 719 Liquid-crystalline polyethers based on conformational isomerism. Part 33.-Thermotropic polyethers based on a mesogenic group containing rigid and flexible units: l-(4-hydroxybipheny1-4-yl)-2-(4-hydroxyphenyl)propane V. Percec, P. Chu, G. Ungar, S.Z. D. Cheng and Y. Yoon 729 Kinetic and mechanistic aspects of iron@) coordination to bipyridyl-based hydrogel polymer membranes A. L. Lewis and .I. D. Miller 735 New route for dispersion of inorganic salts onto the channel surfaces of microporous crystals: high dispersion of CuC1, in zeolites using a microwave technique F-S. Xiao, W. Xu, S. Qiu and R. Xu 741 Determination of acid-base properties of solid materials by inverse gas chromatography at infinite dilution. A novel empirical method based on the dispersive contribution to the heat of vaporization of probes M. M. Chehimi and E. Pigois-Landureau 747 Effect of the position of lateral fluoro substituents on the phase behaviour and ferroelectric properties of chiral 1-methylheptyl 4-[(2-or 3-fluoro-4-tetradecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylates C.J. Booth, D. A. Dunmur, J. W. Goodby, J. S. Kang and K. J. Toyne 761 Free radical generation during thermal decomposition of azoisobutyronitrile in nematic liquid crystal mixtures T. I. Shabatina, Y. K. Yarovoy, V. A. Batyuk and G. B. Sergeev 765 Statistical analysis of apatitic tricalcium phosphate preparation H. Chaair, J-C. Heughebaert, M. Heughebaert and M. Vaillant MATERIALS CHEMISTRY COMMUNICATIONS 771 Conducting polymer-clay composites for electrochemical applications P. W. Faguy, W. Ma, J. A. Lowe, W-P. Pan and T. Brown 773 (BaTi03),(Ge,Ce)3Cu20,: A new homologous series of layered cuprates containing various layers of perovstite units R.Li 775 Corrigendum to effects of sintering conditions on hydroxyapatite for use in medical applications: A powder diffraction study I.Abrahams and J. C.Knowles 775 Corrigendum to preparation and characterization of a sodium insertion compound of hydrogen molybdenum bronze, Nao.2s(HzO),[Ho.21M003] K. Ma, N. Sotani, F. Hatayama, M. Kunitomo and T. Kohmoto 777 Book Reviews: D. Dunmur; R. Whyman; W. Flavell; P. T. Moseley; W. J. Cantwell j Cumulative Author Index ... 111 Subject Group News and Information: Retirement Meeting for George Gray iv 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/JM99404FP041
出版商:RSC
年代:1994
数据来源: RSC
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Back matter |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 043-048
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摘要:
Cumulative Author Index 1994 Abrahams I., 185, 775 Agullo J. M., 695 Akimoto H., 61 Aksay I. A., 353 Chiba K., 551 Chiellini E., 429, 437 Chu P., 719 Ciacchi F. T., 257 Hochi K., 599 Hodby J. W., 469 Hodge P., 1 Holmes P. A,, 365 Mahgoub A. S., 223 Mai S-M., 591 Maireles-Torres P., 179, 189 Malet P., 47 Rodriguez-Castellon E., 179 Rojas R. M., 611 Romanovskaya V. \. ., 373 Ronfard-Haret J-C., 139 Ali-Adib Z., 1 Cole-Hamilton D. J., 657 Holmgren A., 413 Mani R. S., 623 Ross A., 119 Aliev A. E., 35 Coles G. S. V., 23 Hourd A. C., 393 Marcos M. D., 475 Rowatt B., 253 Alves 0. L., 389, 529 Ando M., 631 Connell J. E., 399 Conroy M., 1 Howlin B. J., 379, 385 Hu Y., 469 Marinas J. M., 311 Marks G., 399 Rowley A. T., 285 Rozihe J., 189 Angeloni A. S., 429, 437 Conway L.J., 337 Hudson M. J., 99, 113 Martin T. L., 623 Russell D. K., 13 Annila A., 585 ap Kendrick D., 399 Cook M. J., 209 Cook S. L., 81 Hudson S. A., 479 Hughes A. E., 257 Matsuba T., 599 Matsuda H., 51 Ryan T. G., 209 Sadaoka Y., 663 Ara K., 551 Arai H., 653 Arai K., 275 Aranha N., 529 Armelao L., 407 Cooney R. P., 557 Copplestone F. A., 421 Costa F. M. A., 515 Darriet B., 463 Davidson I. M. T., 13 Huxham I. M., 253 Ikemoto H., 537 Imanishi N., 19 Imayoshi K., 19 Inada H., 171 Maury F., 695 Maza-Rodriguez J., 179 McCarrick M., 217 McGhee L., 29, 119 McMeekin S. G., 29, 119 Sano S., 275 Santiago J., 679 Sastry P. V. P. S. S , 647 Saydam S., 13 Schoonman J., 68'9 Armigliato A., 361 Arnold Jr. F. E., 105 Asaka N., 291 Davies A., 11 3 Deazle A.S., 385 Dekker J. P., 689 Islam M. S., 299 Isoda S., 291 Isozaki T., 237 Mellen R. S., 421 Mendonqa M. H., 515 Merkelbach P., 615 Sergeev G. B., 761 Seron A., 669 Shabatina T. I., 701 Aspin I. P., 385 Attfield J. P., 475, 575 del Arc0 M., 47 Dennison S., 41 Ivanovskaya M. I., 373 James M., 575 Metcalfe K., 331 Miller J. D., 729 Shamlian S. H., 81 Sharma V., 703 Auroux A., 125 Depaoli G., 407 Jimenez R., 5 Mills G. P., 13 Shen D., 105 Azuma K., 139 Baba A., 51 Deschenaux R., 679 Dhas N. A., 491 Jimenez-Lopez A., 179 Jones D. J., 189 Minelli G., 541 Mirtcheva E., 611 Sheng E., 487,68 Sheridan P., 161 Babu G. P., 331 Babushkin O., 413 Diamond D., 145, 217 Drabik M., 265, 271 Jones J. R., 379, 385 Jung K., 161 Miura N., 631 Mizukami F., 585 Sherrington D.C., 229, 253 Shimokawatoko T. 51 Bach S., 133 Drennan J., 245 Kadokawa J-i., 551 Mohanty D. K., 623 Shirota Y., 171, 599 Bachir S., 139 Badwal S. P. S., 257 Dunmur D. A., 747 Eda K., 205,775 Kang J. S., 747 Karasu M., 551 Moretti G., 541 Morpurgo S., 197 Shukla A. K., 703 Simon M., 305 Baetzold R. C., 299 Eguchi K., 653 Kassabov S., 153 Mueller J., 623 Sinclair D. C., 445 Baffier N., 133 Bagshaw S. A., 557 Ekstrand A., 615 Eldred W. K., 305 Kato C., 519 Katsoulis D. E., 337 Murray K. S., 87 Nagae S-i., 591 Singh N., 509 Slade R. C. T., 2h5, 367, Baiios L., 445 Ellis A. M., 13 Kawamura I., 237 Nakano H., 171 501, 509 Barbosa L. C., 529 Barton J. M., 379, 385 Battaglin G., 407 Battle P.D., 421, 641, 707 Etourneau J., 463 Faguy P. W., 771 Fau-Canillac F., 695 Fitzmaurice J. C., 285 Kennedy B. J., 87 King T., 1 Kiyozumi Y., 585 Klissurski D., 153 Nakayama C., 631 Nakayama S., 663 Neal G. S., 245 Neat R. J., 113 Smart S. P., 35 Smith E. G., 331 Smith J. M., 337 Smith M. E., 245 Batyuk V. A., 761 Bautista F. M., 311 Bechgaard K., 675 Fleming R. J., 87 Flint S. D., 509 Foster D. F., 657 Knowles J. C., 185, 775 KO E. I., 651 Kobayashi T., 291 Nicol I., 29 Nishiyama I., 449 Niwa S-i., 585 Snetivy D., 55 Solano Reynoso V C., 529 Solzi M, 361 Bedson J., 571 Fraoua K., 305 Kohmoto T., 205, 775 Nomura R., 51 Sotani N., 205, 775 Beguin F., 669 Bertoncello R., 407 Beveridge M., 119 Bid S., 361 Frederiksen P., 675 Frtalova M., 271 Fuji T., 635 Fujimoto T., 61, 533, 537 Komatsu T., 533, 537 Komppa V., 585 Kossanyi J., 139 Kouyatt D., 139 Nomura S., 171 Nunes M.R., 515 Nygren M., 615 O'Brien P., 565 Spagna A., 437 Stedman N. J., 641, 707 Styring P., 71 Su Q., 417 Bignozzi M. C., 429 Bjarnholm T., 675 Bonardi A., 713 Fukuda A., 237 G. H., 675 Galikova t., 265, 271 KriStofik M., 271 Kubono K., 291 Kubranova M., 265 Ogawa M., 519 Ogura D., 653 Ohnishi K., 171 Suckut C., 5 Sundholm F., 499 Sutherland I., 487, 683 Bond S. E., 23 Galli G., 429, 437 Kunitomo M., 205, 775 Ohta K., 61, 533, 537 Suto S., 631 Booth C., 591 Ganguli P., 331 Kuroda K., 519 Ohtaki M., 653 Suzuki T., 631 Booth C. J., 747 Garcia A., 311 Kuwano J., 9 Oki K., 635 Suzuki Y., 237 Botto L. I., 541 Garcia-Martinez O., 61 1 Lahti P. M., 161 Olivera-Pastor P., 179 Swindell J., 229 Bradley R.H., 487 Branitsky G. A., 373 Brewis D. M., 487, 683 Gatteschi D., 319 Gee M. B., 337 Gibson R. A. G., 393 Landee C., 161 Laus M., 429, 437 Lawrence L. W., 571 Osterlund R., 615 Owen J. R., 591 Pan W-P., 771 TagaT., 291 Tagaya H., 551 Takahashi M., 519 Britt S., 161 Gil-Llambias F-J., 47 Lawrenson B., 393 Pareti L., 361 Takano M., 19 Brock T., 229 Glomm B., 55 Lee C. K., 525 Parkin I. P., 279, 285 Takebe Y., 599 Brodsky C. J., 651 Godinho M. M., 515 Leece C. F., 393 Parsonage J. R., 399 TakedaY., 19 Brown T., 771 Goodby J. W., 71, 747 Lefebvre F., 125 Patil K. C., 491 Takezoe H., 237 Bruce D. W., 479 Gopalakrishnan J., 703 LeGoff P., 133 Pelizzi C., 713 Tan M.P., 525 Bruce P. G., 167 Gozzi D., 579 le Lirzin A., 319 Pennington M., 13 Tarasconi P., 71 3 Bryant G. C., 209 Granozzi G., 407 Le Van Mao R., 605 Percec V., 719 Tetley L., 253 Buist G. J., 379, 385 Gravereau P., 463 Lewis A. L., 729 Pereira-Ramos J-P., 133 Thanapprapasr K., 591 Cairns J. A., 393 Grins J., 445 Li J., 413 Pirez-Jimenez C., 145 Thatcher J. H., 591 Campelo J. M., 311 Guillon D., 679 Li R., 773 Petrov K., 611 Thebault J., 669 Caneschi A., 319 Guo Z., 327 Li X., 657 Pettiti I., 541 Thomas H. J., -541 Cao X., 417 Hamerton I., 379, 385 Lightfoot P., 167 Pic0 C., 547 Thomas M. J. K . 399 Capelletti R., 713 Carlino S., 99 Hams F. W., 105 Harris K. D. M., 35 Linda11 C. M., 657 Lindback T., 413 Picone P.J., 571 Pigois-Landureau E., 741 Thomson J. B., 167 Thorne A. J., 2(@ Carr S. W., 421 Harris S. J., 145, 217 Lindgren M., 223 Porta P., 197, 541 Tian M., 327 Carrazin S. R. G., 47 Haslam S. D., 209 Little F. J., 167 Pottgen R., 463 Toba M., 585 Carvalho A., 515 Cassagneau T., 189 Hatayama F., 205, 775 Heath R. J., 487, 683 Liu C-W., 393 Liu S., 379 Povey I. M., 13 Predieri G., 361 Tomellini M., 579 Tondello E., 407 Cellucci F., 579 Hector A. L., 279 Liu-Cai F. X., 125 Pressman H. A., 501 Torres-Martinez L. M., 5 Cervini R., 87 Heinrich B., 679 Lo Jacono M., 197 Qiu S., 735 Toyne K. J., 747 Cesar C. L., 529 Hermansson L., 413 Lbpez M. L., 547 Ramsaran A., 605 Trigg M. B., 245 Chaair H., 765 Heughebaert J-C., 765 Loubser G., 71 Raynor J. B., 13 Tsuchida T., 631 Challier T., 367 Heughebaert M., 765 Lowe J.A., 771 Rhomari M., 189 Ungar G., 719 Cheetham A. K., 641, 707 Hickey E., 463 Luna D., 311 Richards B. C., 81 Urbana M. R., 311 Chehimi M. M., 305, 741 Chen C., 469 Higuchi A., 171 Hirose N., 9 Lund A., 223 Ma W., 771 Richardson R. M., 209 Rives V., 47 Uzunova E., li3 Vaillant M., 765 Chen Q., 327 Cheng S. Z. D., 105, 719 Chevalier B., 463 Hitchman M. L., 81 Hix G. B., 189 Hobson R. J.. 113 Macklin W. J., 113 Madsen H. G., 675 Maeda K.. 585 Robertson A. D., 457 Robertson M. I., 29, 119 Rockliffe J. W., 331 van der Put P. J. , 689 Van Grieken R., 499 Vancso G. J., 15 i Veiga M. L., 547 Veringa H.J., 689 Vidgeon E. A., 399 Wang H., 417 Wanklyn B. M., 469 Watanabe T., 537 Watts J. F., 305 Wen J., 327 Wessels P. L., 71 Workman A. D., 13 Yamazoe N., 631 Zarbin A. J. G., 389 West A. R., 5, 445, 457, 525, Xiao F-S., 735 Yang H., 55 Zhang W-r., 161 647 Xiao S., 605 Yao J., 605 Zhao L., 623 West D., 1 Westin G., 615 Xu R., 735 xu w., 735 Yarovoy Y. K., 761 Yogo T., 353 Zotov N.. 611 Williams G., 23 Yamamoto H., 635 Yoon Y., 719 Williamson C. J., 565 Yamamoto I., 61, 533, 537 Yoshizawa A., 449 Winfield J. M., 29, 119 Yamamoto O., 19 Yu H., 327 Retirement Meeting for George Gray London,9 February, 1994 On 9 February, over 160 people gathered in London for a meeting, sponsored by the recently formed Materials Chemistry Forum of the RSC, to mark the retirement from full-time research of Professor George Gray FRS.The morning session, chaired by Professor Geoffrey Luckhurst (Southampton), was devoted to the structure of liquid crystal phases with talks on thermotropic systems from Professors John Goodby (Hull) and Alan Leadbetter (Daresbury) and on lyotropic systems from Professor Alfred Saupe (Halle). After lunch, Professor Frank Leslie chaired a session on applications, with talks from Dr Martin Schadt (Hoffmann La Roche), Professor Peter Raynes (Sharp Laboratories) and Professor Harry Coles (Manchester), before handing over to Professor Gray himself who delivered a lecture entitled "A Backward Look and a Forward Glance". A wine reception was followed by a dinner at which the speaker was Professor Cyril Hilsum FRS (GEC).The meeting not only celebrated George's work in liquid crystals but also showed the range of possibilities still open in this vibrant area of research, whose future is obviously assured judging by the attendance of nearly 100 graduate students at the meeting. Pictured above are, left-to-right (front): Professor Alfred Saupe, Professor Frank Leslie, Professor George Gray, Professor Cyril Hilsum, Professor Alan Leadbetter and Professor Harry Coles; (back) Professor Geoffrey Luckhurst, Dr Martin Schadt, Professor Peter Raynes and Professor John Goodby. 111 Conference Diary 1994 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. SSert, EMRS,BP 20,67037 Strasbourg Cedex 2, France. Tel: (33188 10 6543; Fax: (33188 10 6293. June 11-16 Inorganic Chemistry: Surface Organometallic Chemistry, Molecular Materials and Catalysis Davos, Switzerland Dr Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnesia, 67080 Strasbourg Cedex, France.Tel: (33)88 76 7135; Fax: (33)88 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: 914255-0978 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: 5 10-642-9164 June 29July 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 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, 1 Carlton House Terrace, London SWlY 5DB Tel: +44 (0)71235 1391; Fax: +44 (0)71823 1638 July 4-8 20th International Conference on Organic Coatings Science LTechnology 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 Superconductivity/High 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 7NH, UK Tel: +44 (0)227 764-000 ext. 3544; Fax: +44 (01227 475-475 July 6-11 Reactivity in Organized Microstructures: New Materials Mont Sainte Odile, France Dr Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnesia, 67080 Strasbourg Cedex, France. Tel: (33)88 76 7135; Fax:(33)88 36 6987.iv July 11-12 Meeting of the Tetrapyrrole Discussion Group on Chemistry and Biochemistry of Tetrapyrroles London, UK Ray Bonnett or Martin Warren, Queen Mary & Westfield College, Mile End Road, London El 4NS Fax: 071-975-5500 July 11-15 36th International Symposium on Macromolecules: MACROAKRON '94 Akron, Ohio,USA Macroakron '94, Cathy Manus-Gray, Symposium Coordinator, Institute of Polymer Science, The University of Akron, Akron, OH 44325-3909, USA July 19-22 International Conference on Excitonic Processes in Condensed Matters Darwin, Australia Dr J Singh, Faculty of Science, Northern Territory University, PO Box 40146, Casuarina, NT 0811, Australia July 24-29 30th International Conference on Coordination Chemistry Kyoto, Japan Professor H Ohtaki, Laboratories of Coordination Chemistry, Institute for Molecular Science, Myodaiji-cho, Okaz&i 444, Japan July 25-29 36th Microsymposium on Macromolecules Prague, Czech Republic 35th Microsymposium, PMM Secretariat, do Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic July 25-29 International Conference on Synthetic Metals Seoul, Korea Dr C Y Kim KIST, PO Box 131, Cheongryang Seoul 130-650, Korea Fax: 82-2-965-3852 August 1-5 2nd International Conference on f-Elements Helsinki, Finland Professor L Niinisto, ICF'E-2, Conference Chairman, Helsinki University of Technology, Department of Chemical Engineering, Kemistintie 1, FIN-02150 Espoo, Finland Fax: +358-0-462-373 August 2-6 Fourth Asian Conference on Solid StateIonics Kuala Lumpur Secretary, Fourth Asian Conference on Solid State Ionics, do Department of Physics, Faculty of Physical and Applied Sciences, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia August 11-16 Supramolecular Chemistry: 100Years SchlossSchlussel Prinzip Mainz, Germany Dr Josip Hendekovic, European Science Foundation, 1quai Lezay-Marnesia, 67080 Strasbourg, France.Tel:(33)88 76 7135; Fax:(33)88 36 6987. August 2 1-26 1994 ACS National Autumn Meeting Washington DC, USA ACS International Activities Office, 1155 16th St. W,Washington DC 20036, USA August 28- ECM 16, European Crystallographic Meeting September 2 Dresden, Germany Professor P Paufler, Fachbereich Physik, Teknische Universitaet Dresden, Mommsenstrasse 13, D-0-8027 Dresden, Germany Tel: 3378; Fax: 37-51-463-7109 September 4-7 Second European East West Workshop on Chemistry and Energy Sintra, Portugal Cesar Sequeira, Instituto Superior Tecnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal.September 5-7 Electroceramics IV,International Conference on Electronic Ceramics L Applications Aachen, Germany Professor Dr Raker Waser, Institut fur Werkstoffe der Elektrotechnik, RWTH Aachen, D-52056 Aachen, Germany September 5-9 European ESR Meeting on Recent Advances and Applications to Organic and Bioorganic Materials Pans, France Dr Bernard Catoire, GARPE, do ITF-Lyon, BP 60, F-69132 Ecully, France Tel: 78 33 34 55; Fax: 78 43 39 66 September 5-9 6th International Symposium. Scientific Bases for the Preparation of Heterogeneous Catalysts Louvain-la-Neuve, Belgium Dr G.Poncelet, Unit6 de Catalyse et Chimie des Matbriaux DivisBs, Place Croix du Sud, 2 boite 17,1348 Louvain-la- Neuve, Belgium September 6-9 International Conference on Liquid Crystal Polymers Beijing, China Professor Xibai Qiu, Chinese Chemical Society, PO Box 2709, Beijing 100080, China September 7-9 Recent Developments in Degradation and Stabilization of Polymers: Polymer Degradation Discussion Group Brighton, UK Dr NC Billingham, School of Chemistry and Molecular Sciences, University of Sussex, Brighton, BN1 9QJ, UK.Tel: 0273 678313; E-mail: N.Billingham@sussex.ac.uk September 11-14 Ceramic Processing Science and Technology Friedrichshafen (Bodensee), Federal Republic of Germany Deutsche Keramische Gesellschaft e.V., Frankfurter Strasse 196, D 5000 Koln 90, Federal Republic of Germany September 11-14 1lth European Conference on Biomaterials Pisa, Italy Professor Paolo Giusti, 11th European Conference on Biomaterials, Dipartimento di Ingegneria Chimica, Chimica Industride e Scienza dei Materiali Via Diotisalvi, 2-56126, Pisa Italy V September 11-17 1st Euroconference on Solid State Ionics Ionian Sea, Greece Professor Dr W Weppner, Christian Albrechts University, Chair for Sensors and Solid State Ionics, Kaiserstr 2,D-24098 Kiel, Germany September 19-21 8th UK Conference on High-T, Superconductors Birmingham, UK Dr C Greaves, School of Chemistry, University of Birmingham, Birmingham UK, B15 2TT Tel: +44 (0)21414 4397; Fax: +44 (0121 414 4403 September 25-30 International Conference on Molecular Electronics and Biocomputing Goa, India Dr Ratna S Phadke, Scientific Secretary for ISMEBC '94,Chemical Physics Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, INDIA Tel: +91 (22)-215-2971; Fax: +91 (22)-215-2110 October 2-6 66th Annual Meeting of the Society of Rheology Philadelphia, PA, USA Norman Wagner, Dept.Chemical Eng., University of Delaware, Newark, DE 19716 Tel: (302) 831-8079; Fax: (302) 831-10 October 10-12 3rd International Symposium on Structural and Functional Gradient Materials Lausanne, Switzerland FGM '94,Swiss Federal Institute of Technology of Lausanne, Materials Department, LMM, CH-1015 Lausanne, Switzerland Tel: (+41) 21 693 29 15/50; Fax: (+41) 21 693 46 64 October 17-19 1st International Conference on Materials For Microelectronics Barcelona, Spain Conference Department (C421),The Institute of Materials, 1 Carlton House Terrace, London SWlY 5DB, UK Tel:+44 (0)71 839 4071; Fax: +44 (0171 823 1638 October 24-25 International Polypropylene Conference London, UK Ms M Peacock, Conference Department (C4461,The Institute of Materials, 1 Carlton House Terrace, London SWlY 5DB, UK October 24-28 Post-doctoral Course on Degradation and Stabilization of Polymeric Materials Clermont-Ferrand, France Prof.J. Lemaire, Laboratoire de Photchimie, URA CNRS 433,Universite Blaise Pascal, 63177Aubiere Cedex, France. November 14-19 Ionizing Radiation and Polymers Guadeloupe, France Ing. Main LeMoel, SRSIMLPI, CEA CEN Saclay, Batiment 466, F-91191 Gif Sur Yvette Cedex. Tel: (33)1 6908 5485; Fax: (33) 16908 9600. December 19-22 1994 International Conference on Electronic Materials (ICEM'94) & 1994 IUMRS International Conference in Asia (IUMRS-ICA) Hsinchu, Taiwan C/o Materials Research Laboratories, ITRI, Conference Department, IUMRS-ICEIWICA'94,Bldg 77, 195 Chung-hsing Rd, Sec. 4,Chutung, Hsinchu, 3105,Taiwan, ROC. Tel: +886-35-820064, E-mail: 740366@MRL.ITRI.ORG.TW 886-35-916801;Fax:886-35-820247, 886-35-820262; 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 vi
ISSN:0959-9428
DOI:10.1039/JM99404BP043
出版商:RSC
年代:1994
数据来源: RSC
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| 5. |
High-temperature thermoelectric properties of In2O3-based mixed oxides and their applicability to thermoelectric power generation |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 653-656
Michitaka Ohtaki,
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摘要:
J. MATER. CHEM., 1994, 4( 5), 653-656 High-temperature Thermoelectric Properties of In,O,-based Mixed Oxides and their Applicability to Thermoelectric Power Generation Michitaka Ohtaki, Daisuke Ogura, Koichi Eguchi and Hiromichi Arai* Department of Materials Science and Technology, Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga koen, Kasuga, Fukuoka 876 Japan The thermoelectric properties of mixed oxides In,O,~MO,(MO, =Cr203, Mn203, NiO, ZnO, Y203, Nb205,SnOJ are investigated in terms of the thermoelectric materials at high temperature. The Seebeck coefficients, S, of all the samples have negative values, and those of In,O,.SnO, and In,O,.ZnO increase linearly with temperature, attaining values of -90 and -210 pV K-' at 1000 "C, respectively.The electrical conductivities, B, of these oxides are significantly high. The power factor S2a of the oxides has constantly positive temperature coefficients up to over 1000 "C. Rather low thermal conductivities, IC, of the sintered bodies of the oxides, ca. 1.7 W m-' K-' at room temperature, lead to the largest value of the thermoelectric figure of merit Z=0.4 x lov4K-' for M =Sn at 1000 "C, and the Z value increases toward higher temperatures. The Seebeck effect converts thermal energy directly to electrical energy through the thermoelectromotive force gener- ated by a temperature gradient along a solid material. Thermoelectric power generation via the Seebeck effect was proposed in 1940 and was under intensive research until 1960s. However, an energy conversion efficiency sufficient for practical application was not established, and research on thermoelectric power generation ebbed away except in aero- space technologies.Very recently, however, thermoelectric technology has again attracted interest since efficient energy utilization is becoming more and more important owing to concerns about energy resources and the global environment. The efficiency of the thermoelectric energy conversion depends on both the Carnot efficiency qc of the system and the thermoelectric figure of merit Z=S2a/rc of materials constituting the thermoelectric power generating devices, where S, 0and IC are the Seebeck coefficient, and the electrical and thermal conductivities, respectively.Since qc improves the greater the temperature difference over which the device operates, durability to high-temperature operation is desirable for thermoelectric materials. To date, Si-Ge alloys,' several metal ~halcogenides,2,~transition-metal disilicides,- and some boron corn pound^^*^ have been developed as materials for high-temperature thermoelectric power generation. However, practical utilization has been limited because many of them require complicated surface protection to prevent oxidation or vaporization, and some have essential tempera- ture limits due to phase transitions at high temperature. Metal oxides at their common oxidation state seem to be eminently advantageous for high-temperature operation in air, and many of these oxides have high electrical conductivit- ies.Also, there have been extensive studies on the Seebeck coefficients of oxide materials since the Seebeck coefficient is an important and fundamental parameter for evaluating the electrical transport properties of materials. In the studies on physical and chemical sensors, there have been some attempts to utilize the Seebeck effect of oxide materials to detect temperature changes. For example, it has been reported that a 'Seebeck sensor' consisting of an SnO, pellet with a Pt catalyst deposited on one side could detect several flammable gases with voltage output generated by the combustion heat of the gases: although only the magnitude of the Seebeck coefficient is of interest since high electrical conductivity is unnecessary in such applications.Nonetheless, it is surprising that there have apparently been no reports attempting to apply the oxide materials to thermo- electric power generation. While high-temperature super- conducting cuprates were once of interest in application to thermoelectric refrigerators," they had essentially poor performance''. l2 mainly due to their extremely small carrier mobilities (as small as lo-' cm2 V-' s-'). Metal oxides are generally considered to have rather small carrier mobility, partly because of their highly ionic character. However, some oxides have considerably large mobilities. For instance, the reported value of the Hall mobility of Sn02 single csy~tals'~ is 240 cm2 V-'S-' ,and this is much larger than the value14 of 30 cm2 V-'S-' (this is the same as the drift mobility of copper) for ReO,, which shows completely metallic behaviour and the highest electrical conductivity of all the known oxides in the normal state.Indium oxide (In203)is also well known as a highly conductive oxide, and is widely used as sputtered or vapour-deposited thin films for transparent electrodes as indium tin oxide (ITO) which contains several percent of Sn. The high electrical conductivities of these oxides can be attributed to their rather large carrier mobility.'5 In the present paper, we have investigated the thermoelectric proper- ties of several In203-based mixed oxides in terms of the thermoelectric power generation particularly at high tempera- tures.As far as we are aware, this is the first time that metal oxides have been proposed as candidate materials for high- temperature thermoelectric power generation. Experimental Sample Preparation The mixed oxides In203-M0, (MO, =Cr203,Mn203, NiO, ZnO, Y,03, Nb205,SnO,) were prepared from equimolar (on the molecular formula basis) mixtures of the corresponding single metal oxide powders (>99.9%). The powders were mixed and pulverized in a nylon-lined ball mill for 24 h. The powder mixture was pressed into a pellet and sintered at 1400 "C for 10 h in air. The heating and cooling rate was 200 "C h-l. The crystal phases in the samples thus obtained were determined from a powder X-ray diffraction (XRD) study using Cu-Ka radiation.Measurement of Thermoelectric Properties The samples for the electrical measurements were cut out from the sintered pellets as rectangular bars of ca. 15 mm x 5 mm x 3 mm, and polished with Sic emery papers. The measurements of the electrical conductivity and the Pt-Rh/Pt thermocouple -13% +A//I I I ll R sheet Fig. 1 Schematic side view of an experimental set-up for the simul- taneous measurement of the Seebeck coefficient and the electrical conductivity Seebeck coefficient were simultaneously carried out in air from room temperature to 1000 "C. The experimental set-up for the simultaneous measurement is schematically shown in Fig. 1. The CJ values were measured by the dc four-probe technique by using each Pt leg of the thermocouples as a current lead.The current was supplied with a programmable digital-regulated dc power supply, and the potential differences between two voltage probes were measured on a digital voltmeter. The S values were obtained from the least-squares regressions of the thermoelectromotive force as a function of a temperature difference of <5 K applied by a heater at each temperature of measurement. All the measurements were carried out after attaining the steady-state temperature at each step. The thermal conductivity was determined from the thermal diffusivity and the specific heat capacity obtained by the laser flash measurement on ULVAC TC-7000 for sample disks 10 mm in diameter and 1-2 mm in thickness.The data were calibrated with a standard sample of a sapphire single crystal. Results and Discussion Crystal Phases in In,O,-based Mixed Oxides The XRD study revealed that most of the samples of In,O,-MO, consist of two crystal phases, the In,03 phase and the single oxide phase of the counterpart MO,, except for samples combined with Y203, Nb,O5 and Sn0,. The samples of In2O3.Y2O3 and In203.Nb205 were confirmed to be single phases of InYO, and InNbO,, respectively. The mixed oxide In203.Sn02 consists of the In,07 phase and a fairly large amount of an unknown phase, showing no SnO, phase as seen in Fig. 2. Although some diffraction lines in 40 50 60 28ldegrees Fig. 2 Powder X-ray diffraction patterns of In,O,.SnO, sintered at 1400 "C.The lines denoted as unknown (0)can be assigned to the intermediate compound reported in ref. 18. 0 =In203; A = In,Sn,O, -x J. MATER. CHEM., 1994, VOL. 4 Fig. 2 can be assigned to In2Sn207-,,16 most reports on the system 1n2O3-SnO, have discussed that the equilibrium phase at the composition of In,O,/SnO, =1:1 is a simple mixture of a cubic In,O, phase and a tetragonal SnO, phase. Whereas a rhombohedra1 In4Sn3OI2 phase was reported by Bates et all7 to exist at around the composition of In/Sn= 1:1, such a phase has not been confirmed to date. Recently, however, Enoki et all8 reported that in the In,O,-SnO, binary system an intermediate compound exists above 1300 "C in the composition range 47.9-59.3 mol% of SnO,, although the precise composition and the detailed crystal structure of the compound are not clear yet.As indicated in Fig. 2, the diffraction lines of the unknown phase found in our study were very similar to those of the intermediate compound reported there. However, further study should be required to elucidate the phase composition of the mixed oxide In,O,.SnO, in detail. Electrical Transport Properties The Arrhenius plots of the electrical conductivities of In203-M0, shown in Fig. 3(a) indicate that whereas the sample of neat In,O, exhibits metallic behaviour, all the mixed oxides except In,O,.ZnO are semiconducting and have CJ increasing with temperature. The extremely low conductivit- ies for M=Y and Nb would be due to the new mixed oxide phases which could have electrical properties completely different from In,O, and SnO,. On the other hand, the mixed oxide In,03-Sn0, has the highest electrical conductivity of all the samples.In,O,-ZnO is also highly conductive, showing metallic behaviour similar to In203, and the CT values are slightly smaller than those of In203. The slight decrease in CJ would be explained by the lower electron density in In,O,.ZnO due to substitution of trivalent In ions by divalent Zn ions, in accordance with the slight increase in the negative values of the Seebeck coefficient plotted in Fig. 3(b). However, it should be noted that although In,0,.Sn02 also shows a monotonic increase in negative values of S as a i-6 0 1 2 3 4 103 T-W' A A ' - 80 200 0 400 0600 800 31000 77°C Fig.3 Thermoelectric properties of In,03.MOx. (a) The Arrhenius plots of the electrical conductivities, and (b)the temperature depen- dence of the Seebeck coefficients. MO,: @, SnO,; 0, Cr,03;ZnO; 0,A,Mn203; A,NiO; 0,Nb,O,; a, Y203 J. MATER. CHEM., 1994, VOL. 4 function of temperature up to over 1000 "C similar to those of In,O,.ZnO and In,03, the a values of In,O,.SnO, also increase with temperature and exhibit semiconducting behav- iour. Whereas the temperature dependence of cr for M=Sn appears to have a transition point at ca. 500 "C, the relation- ship between log c and 1/T is not linear even in the tempera- ture region higher than the transition point. This means that the steep increase in a above 500 "C cannot be ascribed to the intrinsic region in which both electrons and positive holes are generated by a thermal energy larger than the bandgap energy.Fig. 4 clearly shows that there is a linear relationship between log aT and 1/T, and that the conduction mechanism of In,O,.SnO, is consistent with the hopping conduction of electrons for which the electrical conductivity can be expressed as CT cc1/T exp(-E,/kBT) where E, is the activation energy of the hopping conduction and kB is the Boltzmann constant. In hopping conduction, the thermally activated carrier mobility can lead to a con- stantly increasing electrical conductivity as seen in Fig. 3(a). The activation energy was determined from Fig. 4 as 0.17 and 0.06 eV in the higher and lower temperature regions from the transition, respectively.The power factor S'CTof the samples for the thermoelectric conversion was calculated from the values in Fig. 3, and is shown in Fig. 5. The mixed oxides with SnO, and ZnO had rather large power factor values which increased almost linearly, similarly as for neat In,O,. However, at 1000 "C the values for M=Sn and Zn obviously exceed that of In,O,, owing to the much steeper increase above 800 "C. Changes in the thermoelectric properties of (In203)1 -x (SnO,), with varying composition, x were examined and the maximum value of the power factor was obtained at ca. x=O.5. An increase in x more of than 0.5 resulted in a marked decrease in a, whereas an increase of <0.5 caused 6.0 7 1 4.0 a 1 2 3 4 lo3 T-IIK-' Fig.4 Relationship between log oT and 1/T for In,O,.SnO,. 1.5 I 0.5 -0 00 A' ' o.OLndLAA''' 0 200 400 600 800 1000 77°C Fig. 5 Temperature dependence of the power factor of In,O,.MO,. MO,: 0,SnO,; Ci,ZnO; 8,Cr203; A, Mn203;A,NiO unfavourably small values of S. While the amount of the unknown phase in (In203)1-x (SnO,), estimated in a prelimi- nary study correlated to some extent with the magnitude of the power factor, the behaviour of these two values was not exactly the same, i.e. the amount of unknown phase was greatest for x=O.6. Thus, the maximum of the power factor would be attributable to a mixture of the unknown phase and the In20, phase which attains a optimal combinaticm of S and CT. Thermal Transport Properties and Thermoelectric Figure of Merit The thermal conductivity of In,O,.MO, observed at room temperature was 1.58-1.75 W rn-' K-' for M=In, Sn, Ni, Mn, and Nb, indicating no marked differences among them.Rather low relative density of the samples, namely 65-70%, is presumably responsible for these low and similar values of IC.The temperature dependence of the thermal conductivity of In,O,.SnO, is shown in Fig. 6. The plots reveal that although IC of In,O,.SnO, increases slightly above 500 "C,the value was as low as 3.1 W m-l K-' even at 750 'C. The temperature dependence of the figure of merit Z=S2a/lc of In,O,.SnO, is also plotted in Fig. 6 in which data at and above 800 "C were calculated from the extrapolated kalues of IC.The oxide exhibited an almost linear increase in 2 and attained a value of 0.4 x K-l at 1000 "C without any levelling off.The electrical conductivity of semiconductors increases steeply above the temperature at which the materials show a transition to intrinsic conduction. The thermoelectric: power accordingly diminishes quickly at temperatures higher than the transition point. The figure of merit of the conventional thermoelectric materials thereby usually has a maximum showing an optimal temperature, and decreases beyond this point. However, the temperature dependence of 2 for In,O,.SnO, shows constantly positive temperature coefficients in the whole temperature range up to 1000 "C, and the value is still increasing toward higher temperatures.These results are apparently due to a monotonic increase both in the electrical conductivity and in the thermoelectric power even at very high temperature. Such a tendency has also been reported for B,-,C, for which the hopping conduction mechanism has been ~onfirmed.~,'~ In,03-Sn02 is not single phase, and thus careful investigation of the conduction mechanism of the oxide is necessary; the hopping nature of the conduction revealed in Fig. 4 is probably responsible for the notable thermoelectric properties particularly at high temperatures. Moreover, the higher limit of the operating temperature will be examined in further study; however, In,O,.SnOz and In,O,.ZnO were substantially stable even at 1400 "C'in air..-c 0z -0E 0.2 -4 .c0 o.o<o 0 200 400 600 800 1000 77°C Fig. 6 Thermal conductivity and the figure of merit of In,C),SnO,. J. MATER. CHEM., 1994, VOL. 4 Conclusions The thermoelectric properties of the In,O,-based mixed oxides were investigated. In particular, the mixed oxides In,03-SnOz and In,O,-ZnO at high temperatures exhibited large values of the power factor for thermoelectric power generation. These results are attributed to both the high electrical conductivities and the constantly increasing Seebeck coefficients with increas- ing temperature up to lo00 "C.The promising thermoelectric properties of In,O,.SnO, are presumably due to the hopping conduction of electrons in the oxide with large carrier mobility.The thermal conductivity of In,O,-SnO, was as low as 1.7 W m-' K-' at room temperature, and 3.1 W m-' K-' even at 750 "C. The mixed oxide consequently attained the figure of merit 2 of 0.4 x K-' as the largest value of the samples at lo00 "C. Although the 2 value of the oxide is at present rather small compared with the state of the art of conventional thermoelectric materials, the metal oxides presented here would be hopeful as materials for high-temperature thermo- electric power generation because of their notable thermoelec- tric properties and their excellent durability at high temperatures in air. The authors thank Mr. Yasuhiro Yamada of the Government Industrial Research Institute, Kyushu, for his kind cooperation on the laser flash measurement of IC.One of the authors (M.O.) is grateful to the Kazuchika Okura Memorial Foundation for financial support of this work. References 1 C. M. Bhandari and D. M. Rowe, Contemp. Phys., 1980,21,219. 2 J. C. Bass and N. B. Elsner, Proc. 3rd Int. Conf. Therm. Energ. Conv.,University of Texas at Arlington, Arlington, 1980, p. 8. 3 J. F. Nakahara, T. Takeshita, M. J. Tschetter, B. J. Beaudry and K. A. Gschneidner Jr., J.Appl. Phys., 1988,63,2331. I. Nishida, Phys. Reu. B, 1973,7,2710. I. Nishida and T. Sakata, J.Phys. Chem. Solid, 1978,39,499. T. Kojima, Phys. Status Solidi (a), 1989,111,233. C. Wood and D. Emin, Phys. Rev. B, 1984,29,4582. S. Yugo, T. Sat0 and T. Kimura, Appl. Phys. Lert., 1985,46,842. J. F. McAleer, P. T. Moseley, P. Bourke, J. 0. W. Norris and R.Stephan, Sensors Actuators B, 1985,8,251. 10 W. J. Macklin and P. T. Moseley, Muter. Sci.Eng., 1990, B7, 11 1. 11 T. 0.Mason, Mater. Sci.Eng., 1991, B10,257. 12 W. J. Macklin and P. T. Moseley, Muter. Sci.Eng., 1991, B10,260. 13 C. G. Fonstad and R. H. Rediker, J. Appl. Phys., 1971,42,2911. 14 T. P. Pearsall and C. A. Lee, Phys. Rev. B, 1974,10,2190. 15 S. J. Wen, C. Couturier, J. P. Chaminade, E. Marquestaut, J. Claverie and P. Hagenmuller, J. Solid State Chem., 1992, 101, 203. 16 Powder Diffraction Files, Inorganic Phases, 39-1058, JCPDS International Centre for Diffraction Data 1991. 17 J. L. Bates, C. W. Gril€in, D. D. Marchant and J. E. Garnier, Am. Ceram. SOC.Bull., 1986,65,673. 18 H. Enoki, J. Echigoya and H. Suto, J. Muter. Sci., 1991,26,4110. 19 G. A. Samara, D. Emin and C. Wood, Phys. Rev. B, 1985,32,2315. Paper 3/07624E; Received 30th December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400653
出版商:RSC
年代:1994
数据来源: RSC
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| 6. |
Syntheses of soluble polymeric Lewis bases and their adducts with metal alkyls |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 657-661
Xiaochang Li,
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摘要:
J. MATER. CHEM., 1994, 4(5), 657-661 Syntheses of Soluble Polymeric Lewis Bases and their Adducts With Metal Alkyls Xiaochang Li,t Charles M. Lindall, Douglas F. Foster and David J. Cole-Hamilton* School of Chemistry, University of St. Andrews, St. Andrews, Fife, UK KY76 9ST The pendant double bonds in polybutadiene have been hydrosilated by the reaction of polybutadiene with chloro- dimethylsilane in toluene using H2PtCI, as catalyst. The hydrosilated polybutadiene was further functionalised with 2-picolyl, 4-picolyl, 4-dimethylaminophenyl and diphenylphosphinomethyl Lewis base groups thereby obtaining a series of new polymeric Lewis bases. All the polymers were found to react with group 13 metal alkyls and the 2- or 4-substituted pyridine functionalised polymers were also found to react with group 12 metal alkyls to form soluble polymer adducts.The polymers have been characterised by 'H nuclear magnetic resonance (NMR) spectroscopy, 13C NMR and elemental analysis. Integration of 'H NMR resonances indicates that polymer adducts with M :N or M :P ratios close to 1.O are obtained when using group 13 metal alkyls, whereas polymer adducts with M :N ratios close to 0.5 are obtained when using group 12 metal alkyls. The metal alkyls are easily lost during vacuum drying. The 'H NMR resonances from the alkyl groups on the metal centre shift to a high field upon coordination with N-containing polymeric Lewis bases whilst small downfield shifts are observed upon coordination of Me,M (M=Ga or In) with the P-containing polymeric Lewis bases.Organic Lewis bases that contain electron-donating elements such as 0, N, or P can form adducts with electron-deficient compounds such as group 13 metal alkyls.' These adducts can not only greatly reduce fire and toxicity hazards of the parent metal alkyls, but can also be employed to purify metal alkyls used in metal-organic chemical vapour deposition (MOCVD) through the process of adduct purification.2 Thus, volatile impurities can be removed by evacuation of the isolated adduct at temperatures below its dissociation tem- perature, whilst involatile impurities remain when the adduct is dissociated. By using this approach, different metal alkyls have been purified with adducts containing nitrogen-donor Lewis base?'' and phosphorus-donor Lewis bases.''-13 Although all these systems work fairly well, organic Lewis bases generally have some volatility so that traces of them can contaminate the purified metal alkyls, or can reduce the yield of purified materia1.4,5,10,'4 It has recently been rep~rted'~ that adducts can be prepared between the polymeric Lewis base, poly(viny1pyridine) (PVP), and main-group metal alkyls such as Me,M (n=2, M=Zn, Cd; n=3, M=Al, Ga or In).These adducts dissociate on heating to liberate the metal alkyls and may, therefore, be useful for the purification of metal alkyls and/or for the transport of metal alkyls in a safe manner." The parent metal alkyls spontaneously ignite in air whilst the adducts with PVP are only mildly air sensitive.All of the adducts between Me,M and PVP are insoluble in common organic solvents, largely as a result of the high molecular weight (M,=ca. 330000) of the polymer. This is ideal for the purification or transport of metal alkyls, but there are other applications of this kind of polymeric adduct, such as the formation of nanoparticles by a solution-based route,16 in which it is necessary to have available adducts of metal alkyls with polymeric Lewis bases that can be dissolved in organic solvents. In this paper, we report the synthesis of new polymeric Lewis bases, starting from readily available polybutadienes, together with adducts of these polymeric Lewis bases with main-group metal alkyls. The adducts are all soluble in common organic solvents.t Permanent address: Institute of Material Science and Engineering, East China University of Chemical Technology, Shanghai 200237, China. Experimental Microanalyses were carried out by the University of St. Andrews Microanalytical Service. Nuclear magnetic resonance (NMR) spectra were recorded on Bruker Associates WP80 and AM300 spectrometers operating in the Fourier transform mode with (for 13C)noise proton decoupling. Chemical shifts are in ppm to high frequency of external tetramethylsilane. Differential scanning calorimetry (DSC)was carried out using a Perkin-Elmer DSC 7 instrument and thermal gravimetric analysis (TG) on a Stanton thermal recording balance. All the experiments were carried out under dry, oxygen- free argon, which had been purified by passing it through a column consisting of Cr2+ on silica.Greaseless joints and taps were employed and manipulations were carried out using standard Schlenk-line and catheter-tubing techniques. All the solvents were carefully dried by distillation from so-dium diphenylketyl. 2-Picoline (2-methylpyridine), 4-picoline (4-methylpyridine) and methyldiphenylphosphine were pur- chased from Aldrich and were distilled prior to use. 4-Bromo- N,N-dimethylaniline (Aldrich) was purified by recrystallisation from ethanol. Butyllithium (Aldrich, 1.6 mol dm-3 in hexane) was used as received. Polybutadiene (PB; 83% pendant, 17% trans- 1,4, M, =3000) was a commercial product (Nippon Soda Company) and was used after pumping for 2 h.Me3M, M=Al, Ga or In and Me2M, M=Zn, Cd, were prepared by standard literature method^.^*^*'^ Hy dr osila tion of Polybutadiene The hydrosilation of PB was carried out as described pre- viously'8 but on a larger scale (0.11 mol of double bonds) by the reaction of PB with HSiMe2C1 in toluene (100cm3) in the presence of H2[PtCI6] (0.55 cm3, 0.22 mol dm-3 in propanol) at 80 "C for 22 h. Alkylation of Hydrosilated PB With 4-Lithiomethylpyridine (and 2-Lithiomethylpyridine) 4-Lithiomethylpyridine (and 2-lithiomethylpyridine) was pre- pared by the reaction of butyllithium (70 cm3, 1.6 mol dm-3 in hexane) with 4-picoline (or 2-picoline) (0.11 mol) in tetra- hydrofuran (THF) (150 cm3) at -25 "C according to the 1iterat~re.l~The freshly prepared 4-lithiomethylpyridine (or J.MATER. CHEM., 1994, VOL. 4 2-lithiomethylpyridine) solution (at -25 "C) was added drop- wise, over 1 h, to the solution of hydrosilated PB (0.11 mol Me2SiCl units) in THF (200 cm3) at between -15 and 25 "C with stirring. The resulting red-brown mixture was allowed to warm to room temperature and stirred for a further 12 h before addition of methanol (ca. 15cm3) to hydrolyse any remaining alkylating agent and Si-C1 bonds. The light-yellow solution was poured into water (2.5 dm-3) in order to remove lithium chloride and other impurities. The upper sticky layer was collected and dissolved in CH,C12 (300 cm3). The polymer solution was then washed with distilled water (3 x 100 cmW3), filtered through celite, and evaporated to dryness in uacuo to give a yellow sticky oil [4-picolyl functionalised polybutadiene (4PySiPB) and 2-picolyl functionalised polybutadiene (2PySiPB)I. Yield >95%.With4-Lithiodimethylaminobenzene 4-Bromodimethylaminobenzene (6cm3 of a solution contain- ing 0.14mol in 90cm3 of diethyl ether) was added to the suspension of freshly cut lithium chips (0.3 mol) in diethyl ether (18 cm3) and the resulting mixture heated under reflux conditions for 5-10 min to initiate the reaction.20 The remain- ing 4-bromodimethylaminobenzene was added dropwise over 4 h. After filtration, to remove unreacted Li, the yellow solution was cooled to 0 "C and treated with dropwise addition of hydrosilated PB (0.1 1 mol, Me2SiC1 units) in THF (250 cm3) over 0.5 h.The resulting mixture was allowed to warm to room temperature, stirred for 12 h and treated with methanol (15 cm3) to terminate the reaction. Purification was as described above and the product was obtained as a sticky oil (DMASiPB). Yield >90%. With(Dipheny1phosphino)methyllithium-N,N,N',N'-Tetra-methyl-l,2-diaminoethaneComplex (Dipheny1phosphino)methyllithium-N,N, N', "-tetramethyl-1,2-diaminoethane (TMEDA) complex was prepared by the reaction of butyllithium-TMEDA (0.2 mol) with methyldi- phenylphosphine (0.2 mol) in light petroleum (100 cm3) at room temperature for 72 h according to the literature2' (with 63-67% yield). The freshly prepared yellow powder (0.13 mol, 43 g) was dissolved in THF (150 cm3) and cooled to 0 "C.After adding hydrosilated PB (0.1 1 mol, Me,SiCl units) in THF (200 cm3) dropwise over 0.5 h, the mixture was allowed to warm to room temperature and stirred for 12 h before adding methanol (ca. 10cm3) to terminate the reaction. A similar purification procedure to that described above was carried out to provide the product as a colourless sticky oil (DPPSiPb). Yield >95%. Synthesis of Adducts Between Polymeric Lewis Bases and Metal Alkyls The pure metal alkyl (or a solution of InMe, in THF) was added to a solution of polymer in toluene (ca. 10% w/v) during stirring and at room temperature. The mole ratio of metal alkyl to coordinating atom (N or P) of the polymer was usually 1.5.After stirring for 4 h, the mixture was cooled to -30 "C and the light petroleum added, to precipitate the adduct, before decanting the solvent containing any excess metal alkyl. The adduct was then dried in LUCUO at room temperature for 4-24 h. Results and Discussion Syntheses and Properties of Polymeric Lewis Bases There are two strategies for the synthesis of polymeric bases. The first is by polymerisation of monomers that contain Lewis base groups, the second is by chemical modification of reactive polymers by chemically attaching Lewis base groups to the polymer chain. Interest has been shown in the preparation of new polymers using catalytic functionalisation of polybutadi- enes since these polymers are available with a variety of different microstructures (1,2 or 1,4 addition of butadiene to the growing chain, which leads to double bonds pendant from or contained within the growing chain, respectively), and since the functional groups of interest can often be introduced in a highly selective manner.Examples of functional groups that have been introduced include epo~ides,~~,~~ketone^'^.'^ carboxylic a~ids~~*~~,~~ and Me,SiC13 -n.18*25 Polymers func- tionalised with -SiMe,Cl can then be reacted with 2-lithiomethylpyridine to give polymers with pendant pyridyl gro~ps.'~,~~These polymers have a substituent in the 2-position relative to the pyridyl nitrogen atom so they may suffer from adverse steric crowding when binding to, for example, metal complexes, although it has been shown that it is possible to bind, for example [Fe(CN),]3-.25 Therefore, a similar strategy has been used to synthesize polymers in which the point of attachment to the polymer is in the 4-position relative to the pyridyl nitrogen.In addition, it is known that Me,NC6H4CH,C6H4NMe,6~7 and Ph2PCH2CH2PPh2"-13 are both excellent Lewis bases for the purification of group 13 metal alkyls. We have, therefore, synthesized polymeric analogues of these compounds by reacting polymer bound -CH,SiMe,Cl groups with 4-LiC6H4NMe2 and LiCH,PPh,, respectively. For all of these polymeric Lewis bases, a PB with a high (83%) pendant double-bond content has been used because the hydrosilation reaction occurs preferentially on the pendant double bonds and with a relatively low molecular weight (M,=3000) so as to retain solubility for the polymeric Lewis bases in common organic solvents.In order to avoid crosslinking and gel formation, it is necessary to use excess SiMe,HCl during the hydrosilation reaction and excess lithium reagent during further functionalisation. The synthetic reactions are outlined in Scheme 1. The polymeric Lewis bases have all been characterised by their 'H and 13C NMR spectra (Table 1) and by microanalysis (Table2). In all cases, small amounts of unreacted pendant double bonds are present in the polymer but all -SiMe2C1 groups are converted to -SiMe2L (L=2- or 4-CH,C5H4N, -C6H,NMe2 or CH,PPh2). In some cases, there are small resonances close to the main resonance from the Me,% groups.These may arise from a small amount of hydrosilation of the backbone double bonds or, more likely, from the presence of traces of degraded polymer (see below). Table 1 'H (and 13C)NMR results for polymeric Lewis bases" polymer SiCH, SiCHz CH=CH polymer CH, CH2 base group 2PySiPB -0.05 (-4.0) 0.40(10) 5.30 (128, 132) 1.0-2.0(27, 34, 38) 2.3, 6.9, 7.45, 8.35(119, 122, 135, 149, 161) DMASiPB 0.2 (-2.8) 0.6 (11) 5.3(129, 132) 4PySiPB -0.1 (-4.0) 0.40(10) 5.30(128, 132) 1.0-1.9(27, 34, 38) 1.0-2.0(27, 34, 38) 2.5, 6.7, 7.4(40, 112, 135, 151) 2.0(26), 6.8, 8.3(123, 149, 150) DPPSiPB -0.1 (-2.0) 0.4 (13) 5.4 1.0-2.0(27, 34, 38) 1.4, 7.2, 7.4(128, 132, 141) "In CdC13 at 298 K; chemical shifts in ppm.assignment -CH2-2Py -CH2-4Py -C,H,-NMe, -CH,P(C& J. MATER. CHEM., 1994, VOL. 4 + HSiMe2CI HdPtCIG] in toluene-80“C, 22 h + LCHZ + LiCHzG N + LiCHz-P(CGH5)z*Th4EDA CH3-Si-CH3 I CI 1c 2PySi PB CH3-Si-CH,I 4pYSiPB CH3-Si-CH,I DMASiPB CH3-Si-CH,IQ N CH3’ ‘CH3 DPPSiPB CH3-Si-CH3 I Scheme 1 Synthesis of polymeric Lewis bases Table 2 Elemental analysis results of polymeric Lewis bases polymeric Lewis bases measured value (%) C H N calculated value (%y C H N 2PySiPB 4PySiPR DMASiPB 69.36 69.65 71.02 10.89 11.17 9.40 5.36 4.83 5.00 70.19 70.19 72.83 9.02 9.02 9.92 6.93 6.93 5.73 DPPSiPB 73.67 8.48 0.00 73.60 8.12 0.00 “Assuming all pendant double bonds are converted to Lewis bases, as in Scheme 1.All the polymers are sticky oils that are soluble in common organic solvents of medium polarity such as diethyl ether, THF, CH,Cl, and toluene. They are stable if stored in THF or diethyl ether in the dark but we find that in the light, especially in the absence of solvent, all of the polymers decompose to give insoluble resins presumably vra a cross- linking reaction. The order of stability of the polymeric Lewis bases is -C,H,NMe, >2-CH,C5H4N >CH ,PPh, >4-CH,C,H,N. Because of the low stability of the 4-pyridyl functionalised polymer, we have studied this in more detail. Studies by ‘H NMR of this polymer in CDC1, show that over a period of days the signals from the -CH2C5H4N attached to the silicon atoms of the polymer decrease in intensity whilst J.MATER. CHEM., 1994, VOL. 4 B7 7 BI MA B = (CH312Na I (c6H5)2p4H2-B = -CH2a, 4 H 2 G MA = InMe3, GaMe3, AIMe3, CdMe2, ZnMe2 M = Cd, Zn Fig. 1 Structures of adducts between polymeric Lewis bases and metal alkyls new resonances from free 4-methylpyridine increase. At the same time, the resonance from the methyl groups on silicon decreases in intensity whilst a new resonance increases at 6 0.0. We tentatively conclude that a photochemical crosslink- ing reaction, which releases free 4-methyl pyridine, occurs. Similarly, samples of -CH,PPh, functionalised polymers also lose Ph,MeP when they are allowed to stand in the light, particularly in the dry state.Nevertheless, all the polymers can be stored for months in THF solution in the dark or for up to 3 weeks in the dry form in the dark. DSC and TG of the polymers under nitrogen show that they are generally stable up to 200 "C (300 "C for -CGH,NMe2) but that above this temperature they start to decompose, darkening in colour and losing weight. Adducts with Main-group Metal Alkyls As expected, all of the polymeric Lewis bases react with Me,M to give adducts. For L=-C,H,NMe, or -CH,PPh, only reactions with Me,M (M=Al, Ga or In) were successful? whilst for L =2-or 4-CH2C5H,N, adducts were prepared with Me,M' (M'=Zn or Cd) and Me3A1. In all cases, the adducts formed from toluene, THF or diethyl ether were soluble in common organic solvents so their stoichiometries could be determined from 'H NMR studies.A check was also made by measuring the change in the weight of the polymer on adduct formation, although this method is unreliable because: (i) not all of the polymer may be collected after precipitation; (ii) it is difficult to remove the last traces of solvent from the polymers; and (iii) dynamic vacuum can remove some or all of the coordinated metal alkyl even at room temperature. The NMR studies suggest that the adducts of -CH,C,H,NMe, with Me,M, M=Al, Ga or In have a j. For L=-C,H,NMe,, reactions with Me,M' (M'=Zn or Ca) give products that contain only traces of the metal alkyl (<5%). limiting 1 :1 M :N ratio, although for Ga and In the observed ratio is generally less than this because prolonged pumping on the isolated adducts to remove residual traces of solvents also removes some of the metal alkyl.For Me,AI, the binding to the polymer is stronger as evidenced by (i) no loss of Me,Al on prolonged pumping at room temperature and (ii) the observation that the solution warms noticeably during the formation of this adduct whereas this is not the case for the other metal alkyls. For the adducts of polymers containing 2-CH2Py or 4-CH2Py with Me,M' (M'=Zn or Cd), NMR studies on isolated and vacuum-dried compounds show that only traces of the metal alkyl are present, although if an adduct is prepared in solution, precipitated and its 'H NMR spectrum run without having dried the sample, the Me,Zn :pyridine ratio is 0.5: 1, as has been observed for adducts of Me2Zn with small N donor Lewis ba~es,4*~,'.~ which include pyri- dine.30 The nature of the adducts is shown in Table 3 and their proposed structures in Fig.1. Table 3 Preparation and properties of polymeric adducts M/Nratio Solubility"adducts appearance 2PySiPB/Me2Cd yellow resin 2PySiPB/Me,Zn yellow solid 2PySiPB/Me,Al yellow solid 4PySiPB/Me2Cd light-yellow solid 4PySiPB/Me2Zn light-yellow solid 4PySiPB/Me,Al yellow solid DM ASiPB/Me,Ga yellow resin DM ASiPB/Me,In yellow resin DM ASiPB/Me,Al white solid DPPSiPB/Me,Ga transparent resin DPPSiPB/Me,In transparent resin DPPSiPB/Me,Al transparent resin a~:soluble; x: insoluble. Table 4 'H NMR measurement of polymeric adducts (ppm)" adducts 2PySiPB/Me2Cd 2PySiPB/Me2Zn 2PySiPB/Me,AI 4PySiPB/Me,Cd 4PySiPB/Me2Zn 4PySiPB/Me,Al DMASiPB/Me,In DM ASiPB/Me,Ga DMASiPB/Me,Al DPPSiPB/Me,In DPPSiPBjMe,Ga DPPSiPB/Me, A1 "In C2H,]benzene Si-CH, CH =CH 0.0 5.40 0.0 5.42 0.0 5.42 0.0 5.42 0.0 5.38 0.0 5.40 0.2 5.38 0.2 5.42 0.2 5.48 -0.1 5.5 -0.1 5.5 -0.1 5.5 base group M-CH, 0.5 toluene(v), THF(v) 0.5 toluene(v), THF(v) 1.o toluene(v), THF(v) 0.5 toluene(x), THF(v) 0.5 toluene (x), THF( v) 1.o toluene(x), THF(v) 1.o toluene(v), THF(v) 1.o toluene(v), THF(v) 1.o toluene(v), THF(v) 1.o toluene(v), THF(v) 1.o toluene(v), THF(v) 1.o toluene(v), THF(v) M-CH,( free) 2.34, 6.95, 7.48, 8.30 -0.62 -0.53 2.32, 6.95, 7.48, 8.40 -0.82 -0.63 2.35, 6.96, 7.50, 8.40 -0.93 -0.34 2.15, 6.95, 8.40 -0.67 -0.53 2.10, 6.90, 8.30 -0.72 -0.63 2.25, 7.14, 8.38 -0.85 -0.34 2.35, 6.5, 7.35 -0.25 -0.23 2.30, 6.70, 7.32 -0.40 -0.12 2.30, 6.95, 7.35 -0.70 -0.34 1.20, 6.90, 7.28 -0.10 -0.23 1.10, 6.90, 7.20 -0.10 -0.12 1.28, 7.15, 7.35 -0.40 -0.34 at 298 K except the 4PyPB adducts, which were in ['H,]THF.J. MATER. CHEM., 1994, VOL. 4 66 1 All of the polymeric adducts are soluble in THF and all except those containing 4-CH2Py are soluble in aromatic solvents. 'H NMR studies (Table 4) show that the resonances from the polymer backbone are unaffected by adduct forma- tion whilst those from the donor groups shift to a higher field on account of the removal of electron density by the Lewis 6 7 8 9 D.F. Foster, S. A. Rushworth, D. J. Cole-Hamilton, A. C. Jones and J. P. Stagg, Chemtronics, 1988,3,38. D. F. Foster, S. A. Rushworth and D. J. Cole-Hamilton, UK Pat., 8 704 657,1987. H. M. Yates, J. 0. Williams, I. L. J. Patterson and D J. Cole- Hamilton, J. Cryst. Growth, 1993,129,215. D. F. Foster, I. L. J. Patterson, L. D. James, D. J. Cole-Hamilton, acid. The alkyl resonances shift to a high field on coordination with N-containing Lewis bases but to a low field when Me,Ga or Me& are bound to the -CH2PPh2 functionalised polymer. In contrast to the free metal alkyls, the polymeric Lewis base adducts are non-pyrophoric and only slightly air sensi- tive. DSC and TG studies suggest that they all dissociate on 10 11 12 D.N. Armstrong, H. M. Yates, A. C. Wright and J. 0. Williams, Adv. Muter. Opt. Electron., 1994,3, 163. D. F. Foster, S. A. Rushworth, D. J. Cole-Hamilton, R. Cafferty, J. Harrison and P. Parkes, J. Chem. Soc., Dalton Trans., 1988,7. D. C. Bradley and H. Chudzynska, Polyhedron, 1988,7, 1289. A. H. Moore, M. D. Scott, J. I. Davies, D. C. Bradley, M. M. Faktor and H. J. Chudzynska, J. Cryst. GroKth, 1986, heating to liberate the metal alkyl so that they may be suitable for purification of the metal alkyls. However, since the adducts liberate substantial amounts of metal alkyl when they are pumped in uacuo for removal of solvent residues, and since the polymeric Lewis bases themselves decompose on heating above ca. 200 "C, their application for purification is limited.13 14 15 16 77, 19. D. C. Bradley, H. Chudzynska and M. M. Faktor, Uorld Put., 04405,1985. K. H. Thiele, Z. Anorg. Allg. Chem., 1964,330, 8. X. Li, D. F. Foster and D. J. Cole-Hamilton, Polym. Adv. Technol., in the press. V. Saukarau, J. Yue, R. E. Cohen, R. R. Schrock and R J. Sibley, Indeed, attempts to liberate pure metal alkyls from them have led to only low recoveries (30%). The fact that the adducts are soluble in organic solvents (in contrast to the PVP adducts) means that they are much more suitable for studies of their reaction chemistry. We are, therefore, studying the use of these polymeric adducts for the production of a wide range of nanoscale particles of a variety of semiconducting materials.,l 17 18 19 20 21 22 Chem.Muter., 1993,5, 1133. D. F. Foster and D. J. Cole-Hamilton, Inorg. Synth., in the press. A. Iraqi, S. Seth, C. A. Vincent, D. J. Cole-Hamilton, M. D. Watkinson, I. M. Graham and D. Jeffrey, J. Matm. Chem., 1992, 2, 1057. 0.F. Beumel, W. N. Smith and B. Rybalka, Synthesis, 1374,1,43. W. Kaminski and D. L. Esmay, J. Org. Chem., 1960,25, 1870. N. E. Schore, L. S. Benner and B. E. Labelle, Inorg. Chem., 1981, 20,3200. M. Gahagan, A. Iraqi, D. C. Cupertino, R. K. Mxkie and We thank the Japanese Soda Company for the gifts of polybutadiene, the Royal Society for a K. C.Wong Fellowship 23 24 D. J. Cole-Hamilton, J. Chem. SOC.,Chem. Commun., 1989, 1688. A. Iraqi and D. J. Cole-Hamilton, Polyhedron, 1991, 10. 993. P. Narayanan, B. G. Clubley and D.J. Cole-Hamilton, J. Chem. (X.L.) and SERC for Fellowships (C.M.L. and D.F.F.). 25 Soc., Chem. Commun., 1991, 1628. A. Iraqi, M. Watkinson, J. A. Crayston and D. J. Cole-Hamilton, J. Chem. SOC., Chem. Commun., 1991, 1767. References 26 27 A. Iraqi and D. J. Cole-Hamilton, J. Muter. Chem., 1992,2, 183. P. Narayanan, A. Iraqi and D. J. Cole-Hamilton, J. Ma!er. Chem., 1 D. G. Tuck, in Comprehensive Organometallic Chemistry, ed. 1992,2, 1149. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon, Oxford, 28 P. Narayanan, B. Kaye and D. J. Cole-Hamilton, J. Maaer. Chem., 1982, vol. 1, p. 683. 2 D. J. Cole-Hamilton, Chem. Br., 1990, 852. 29 1993,3, 19. X,Guo, R. Farwaka and G. L. Rempel, Mucromolecriles, 1990, 3 P. R. Jacobs, D. V. Shenai-Khatkhate, E. D. Orrell, J. B. Mullin 23, 5047. and D. J. Cole-Hamilton, UK Put. 8 509 055, 1985. 30 G. Levy, P. de Loth and F. Gallais, C.R. Acad. Sci., Ser. C., 1974, 4 P. R. Jacobs, E. D. Orrell, D. V. Shenai-Khatkhate, J. B. Mullin 278,1405. and D. J. Cole-Hamilton, Chemtronics, 1986, 1, 13. 31 X. Li, D. F. Foster and D. J. Cole-Hamilton, in preparation. 5 D. V. Shenai-Khatkhate, E. D. Orrell, J. B. Mullin, D. C. Cupertino and D. J. Cole-Hamilton, J. Cryst. Growth, 1986,77,38. Paper 3/07521D; Received 22nd December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400657
出版商:RSC
年代:1994
数据来源: RSC
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Preparation of Na3Zr2Si2PO12–sodium aluminosilicate composite and its application as a solid-state electrochemical CO2gas sensor |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 663-668
Susumu Nakayama,
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摘要:
J. MATER. CHEM., 1994,4(5), 663-668 Preparation of an Na,Zr,Si,PO,,-Sodium Aluminosilicate Composite and its Application as a Solid-state Electrochemical C02 Gas Sensor Susumu Nakayama" and Yoshihiko Sadaokab a New Materials Research Center, Shinagawa Refractories Co. Ltd., Bizen, 705 Japan Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama, 790 Japan A composite of sodium aluminosilicate and Na,Zr,Si,PO1, has been examined as a dense solid-state sodium-ion conductor. For the composite sintered at 1050 "C, the electrical properties are mainly based on those of Na3Zr2Si2PO12. When the composite was sintered at a higher temperature, the activation energy of the resistance increased to ca. 55 kJ mol-' and the densification was well progressed with the formation of small zirconia particles.A good junction between the composite and Y-stabilized zirconia was achieved when the sintering was carried out at 31175 "C. The formation of zirconia particles in the composite layer resulted in an enhancement of the mechanical strength at the junction. By using the ceramics, a solid-state electrochemical CO, sensor with an Na,CO, layer was fabricated. Whilst the sensitivity of this sensor to CO, was slightly influenced by the coexistence of the water vapour in the test gas, a good sensing characteristic based on two-electron electrochemical reaction was confirmed. The discovery of Na3Zr,Si,PO12 represented an important development in the field of solid electrolytes because it demon- strated that a three-dimensional framework structure could have a conductivity comparable to that of b-alumina, a two- dimensional network.Recently there has been interest in solid glass electrolyte^.'-^ Glasses present several advantages over crystalline materials for solid-state electrolyte and/or chemical sensor application^.^.^ Hunter and Ingram examined sodium- ion conduction in glasses, including silicates and borates, and found that the conductivity increases with optical basicity, whilst the activation energy falls towards an apparent limiting value of ca. 50 kJ mol-1.8 Similar results were reported by Hakim and Uhlmann.g The ceramics obtained by the sintering of a mixture of Na,Zr,Si,PO,, and sodium aluminosilicate indicated that the high ionic conductivity and its activation energy was lowered to ca.50 kJ mol-' and the densification was well pr~gressed.~ Both materials are superior in respect of water resistivity. This paper presents the results of a study of using the title composite to prepare a dense ionic conductor for a solid-state electrochemcial CO, gas sensor. Experimental Crystalline Na,Zr,Si,PO,, powder was made from reagent- grade Na,CO,, NH4H,P04, ZrO, and SiO, using conven- tional ceramic techniques. The mixture of raw materials was ball-milled with ethanol, dried at 100 "C, calcined in air for 4 h at 900 "C, then ground. Pellets were pressed at 1000 kg cmP2 and sintered at 1250 "C in air for 15 h. Na,Zr,Si,PO,, powder was prepared by milling the prepared ceramics (mean particle diameter z1 pm).Na,O-Al,03-4Si02 was made from reagent-grade Na,C03, Al,03 and SiO, by sintering a mixture at 1350 "C. The powders were also obtained by milling. A mixture of Na,Zr,Si,PO,, and 40 wt.% Na20-A1,O3-4SiO2 was compressed and sintered at 1000 "C. ZrO, discs with 8 mol% Y203 were also sintered at 1600 "C. The discs were 10 mm in diameter and ca. 1 mm thick. The sodium-ion conductors were placed on the ZrO, discs and sintered at various temperatures. The crystalline phases were identified at room temperature by the standard X-ray diffraction technique (XRD). The microstructures were examined using scanning electron microscopy (SEM). The electrical properties of discs in which platinum paint acted as electrodes (applied to opposite faces by sintering at 800 "C) were measured using an LCZ meter (100 Hz-10 MHz).A disc with porous platinum electrodes was fixed on the top of an alumina tube with an inorganic adhesive containing sodium. The electrode inside the tube acted as the reference electrode. The platinum sensing elec- trode was positioned on the outside face of the disc, covered with Na,C03 and then dried at 80 "C. Standard gases, air (CO<1 ppm, CO, <2 ppm, HCl < 1 ppm and H,O < 10 ppm) or CO, at 10, 100, 1000 and 10000 ppm diluted with air, were introduced to the working (sensing) electrode side. Humidification of the test gas was achieved by allowing the test gas to bubble through water at 30 "C. The emf of the sensor was measured with a digital electrometer.Results and Discussion Form of Electrolytes Some sodium aluminosilicates prepared by calcination at 1000 "C were examined by XRD. Na,0-A1,03-2Si0, was identified as carnegieite (low form) and no distinct glass phases were detected. For Na,O-Al2O,-4SiO,, the broad band caused by the glass phase and some weak diffraction peaks were detected. For Na,O-Al,O,-nSiO, (n=6 and 8), strong peaks assigned to a-quartz were detected at ti =0.4262 and 0.3343 nm with a broad band. In addition, NASICON was identified in its monoclinic form with ZrO, as an impurity. Previously it was confirmed that when the composites were sintered at 1000 "C, a well densified composite of N.4SICON and Na20-A1,03-4Si0, was obtained for a mixlure with 40 wt.% of Na,O-Al,O,-4SiO2.In this work, a NASICON-glass composite was prepared from a mixture of NASICON with 40 wt.% Na,0-A1,03-4Si0,. The XRD parameters are summarized in Table 1. For the composite sintered at 1050 "C, the observed XRD pattern is very similar to NASTCON singly and the peaks observed for the Na20-A1,03-4Si02 were not detected. When the sintering temperature is increased to 1150 "C, peaks assigned to NASICON were observed and the intensity of the peaks assigned to ZrO, (d=0.316, 0.284 and 0.262 nm) increased with increasing sintering temperature. For samples sintered at 31175 "C, the XRD pattern changed completely, i.e. the disappearance of the signals assigned to NASI(10N and growing-in of the ZrO, signals were observed. The correlation between the ratio of the intensity, I(d=0.294 nm)/l(d= 0.316 nm) and the sintering temperature is shown in Fig.1 in J. MATER. CHEM., 1994, VOL. 4 Table 1 Relative intensities of some XRD peaks sintering temperature/"C composite NASICON d/nm 1200 1050 1100 1125 1150 1175 1200 ~ 0.6510 0.55 0.51 0.52 0.53 0.39 0.09 0.4643 0.94 0.91 0.93 0.96 0.64 0.4520 1.oo 0.99 0.99 1.00 0.69 0.3890 0.52 0.53 0.54 0.55 0.42 0.3694 0.11 0.18 0.24 0.26 0.31 0.25 0.26 0.3233 0.68 0.65 0.67 0.70 0.49 0.3166 0.12 0.34 0.57 0.56 1.00 1.00 1.00 0.2932 0.98 1.00 1.00 0.98 0.70 0.2840 0.12 0.29 0.41 0.51 0.68 0.67 0.71 0.2613 0.36 0.32 0.36 0.36 0.33 0.27 0.25 0.2608 0.74 0.74 0.82 0.85 0.69 0.2542 0.07 0.15 0.18 0.21 0.24 0.21 0.21 0.2495 0.07 0.10 0.12 0.11 0.12 0.09 0.10 Fig.1 Correlation between Z(d =0.294 nm)/Z(d=0.316 nm) and the sintering temperature of the mixture of NASICON and 40 wt.% Na20-A120,-4Si02 which the peaks at d=0.294 and 0.316nm are attributed to NASICON and ZrO,, respectively. The changes in the microstructure were also examined by SEM (Fig. 2). For the NASICON singly, monoclinic crystal- lites 1-2 pm in size were detected. Interfusion of the particles was only partial. The surface of the Na,O-Al,03-4Si0, glass prepared by sintering at 1000 "C was very smooth and there were hardly any detectable pores and/or holes. When a mixture of Na20-A1,O3-4SiO2 glass and NASICON was sintered at 1050 "C, the surface was covered by a glass-like phase and no crystalline phase could be directly observed.It seemed that the NASICON particles were covered by the glass phase whilst XRD signals assigned to NASICON were detected, as mentioned above. When the sintering temperature was increased to 1100 "C, the densification by the glass phases was well progressed, with the formation of cubic-like crystals, whilst the presence of the NASICON particles was detected. The size of the newly formed crystals was smaller than that of the NASICON used as the starting material. The newly detected finer crystals were ascribed to ZrO,. With an increase in the sintering temperature, the formation of ZrO, particles and new glass-like phases were accelerated and the NASICON phase disappeared.When the composite was sintered at 211 75 "C, interfusion of the glass phases proceeded and small closed pores of 0.5-1 pm diameter were observed. The results of the XRD and SEM observations confirm that the NASICON layer reacts with the glass layer and the formation of ZrO, proceeds when the temperature is increased to ca. 1100 "C. Furthermore, to obtain a good junction between the com- posite and the Y-stabilized zirconia disc, the composite disc prepared by sintering at 1000 "C was placed on the zirconia disc and calcined at various temperatures. When the tempera- ture was increased to ca. 1125 "C, cracks formed in the composite disc parallel to the connected surface. For the samples heated at 31150 "C cracks were not detected and each layer was well connected; in addition, the composite disc was softened and partly melted when the temperature was increased to 3 1175 "C.Fig. 3 shows photomicrographs of the fractured faces. For samples sintered at d 1125 "C, no new phases were detected at the junction. When the sample was sintered at 1200 "C, a new phase/layer was detected at the junction. We tried to obtain a good junction between NASICON and Y-stabilized zirconia by sintering at 1200 "C, but an adequate junction could not be obtained. Further detailed experiments on the junction are now in progress. For samples calcined at 31175 "C, the junction does not undergo peel-off or removal and is stable to mechanical and/or thermal shock. The observed properties are sufficient for a solid-state electrochemical CO, gas sensor coated with an Na2C03 layer and with platinum electrodes on the surfaces to be fabricated.These changes in the composite and the enhancement of the mechanical strength of the junction are attributed to the formation of a layer of ZrO, and new glass-like phases in the composite layer and the appearance of this new layer at the junction. Electrical Properties For the composites, the equivalent total electrical resistance is made up from several components such as the intergranular, bulk and electrode-electrolyte junctions. For the Na,O-A1203-4Si0, glass prepared by sintering the mixture at 1000 "C, the complex impedance plot is represented by an arc which passes through the origin.In this case the resistance, which can be estimated from the intercept (Rglass)to the Z'-axis in the low-frequency region, is attributed to the glass phase. Similar features in the complex impedance plots were observed for the composite prepared by sintering at 1200 "C in which the resistivity of the glass phase was estimated from the intercept to the 2'-axis at low frequency. The complex impedance plots for NASICON are shown in Fig. 4. At a low temperature, the complex impedance is represented by an arc in the high-frequency region and by a spur in the low- frequency region. The intercepts (denoted A and B in the figure) to the Z-axis indicate the resistances of the bulk component @bulk) and of the sum of the bulk and grain components (Rbulk+ Rgrain),respectively.When the tempera- ture was high, only the spur was observed, in which the intercept (B) to the Z-axis indicates the sum of the bulk and grain components. For the composite sintered at 1050 "C,the complex impedance plot was more complex (Fig. 5), while only a spur was observed at 250 "C. At 80 'C the high- frequency region was represented by an arc and the low- frequency region by the combination of an arc and a spur. When the temperature was increased to 150 C, the result was represented by the combination of an arc and a spur. The intercept (C) to the 2'-axis of the spur is attributed to the total equivalent resistance (Rbul,+ Rgrain+ Rglass). The values estimated from the intercepts (A, B, C) for the composite at 80 "C corresponded to the bulk (Rbu]k), the sum of the bulk and grain components based on NASICON (Rb,]k + Rgrain) and the sum of Rbu1k, Rgrainand the resistance of glass phase J.MATER. CHEM., 1994, VOL. 4 Fig. 2 Scanning electron micrographs: (a) NASICON sintered at 1200 "C, (b)Na20-A120,-4Si02 sintered at 1000 'C, (c) composite sintered at 1050 "C, (d)composite sintered at 1100 "C, (e)composite sintered at 1150 "C, (f)composite sintered at 1175 "C (Rglass),respectively. From the result observed at 150 "C, where R is the resistivity, R, is the pre-exponential factor, E, (Rbulk +Rgrain)and (Rbu&+Rgrain+Rglass)could be estimated. is the activation energy, kB is the Boltzmann constant and T The temperature dependence of the estimated resistivity is is the absolute temperature.shown in Fig. 6. The results were parametrized by the The activation energy of the resistivity estimated from Arrhenius equation: (Rbulk +Rgrain) of the composite sintered at 1050 "C was comparable to that of NASICON alone. Furthermore, the RT-' =R, exp(E,/k,T) (1) activation energy of the resistivity estimated from Kglasswas J. MATER. CHEM., 1994, VOL. 4 Fig. 3 Scanning electron micrographs of the fractured faces of the (a) 1100 "C, (b) 1200 "C 0 0 0 B A E ,?'(arb. units) Fig. 4 Complex impedance plots of NASICON: (a) 50 "C, (b)200 "C A B B cc Z'(arb. units) Fig. 5 Complex impedance plots of the composite sintered at 1050 "C: (a) 80 "C, (b)150 "C composite-Y-stabilized zirconia junction.Sintering temperature: 4r -3 1.o 1.5 2.0 2.5 1O~WT Fig. 6 Temperature dependence of the resistivities: (Rbulk+Rgrain)of NASICON (a), (Rbulk+Rgrain)of composite sintered at 1050 "C (b), Rglass of composite sintered at 1050 "C (c), Rglass of Na,0-A1203-4Si02 sintered at 1000 "C (d), Rglass of composite sintered at 1200 "C (e) comparable to that of the Na20-Al2O3-4Si0, glass prepared by sintering the mixture at 1000 "C and/or of the composite sintered at 1200 "C.These correlations confirmed the results of XRD and SEM observations. The complex impedance plots for the Y-stabilized zirconia are shown in Fig. 7. A spur in a low-frequency region and an arc which passed through the origin in the complex impedance plot were observed at <300 "C.The intercept (A) to the 2'-axis is attributed to the bulk component.At a higher tempera- ture, two arcs and a spur were observed and the arc in the high-frequency region passed through the origin." The two values (A and B) extrapolated to the Z'-axis are attributed to the bulk component in the resistance and the sum of the bulk and grain components in the resistance, respectively. The complex impedance plots for the Y-stabilized zirconia connected with the composite are shown in Fig. 8. The complex impedance plot was represented by an arc which passed through the origin and spur at 250 C. At a high temperature, ca. 300 "C, two arcs were clearly observed in J.MATER. CHEM., 1994, VOL. 4 A 0 00"aa O-I I I A €3 A Z'(arb. units) Fig. 7 Complex impedance plots of Y-stabilized zirconia: (a) 300 "C, (b)450 -C 1; (b) 0 I I I I A AB Z'(arb. units) Fig. 8 Complex impedance plots of the composite connected with zirconia sintered at 1200 "C: (a) 250 "C, (b)400 "C which the arc observed at high frequency passed the origin. At higher frequency two intercepts (A and B) to the Z-axis are expected. The first intercept, A, corresponds to the bulk component to the resistance and the second, B, to the sum of the bulk and grain components to the resistance. At higher temperature, an arc and a spur were present and two intercepts were expected. The lower value of Z' corresponds to the bulk component and the other to the sum of the bulk and grain components.From these observations, the resistivity for each component was estimated and the temperature dependence of the resistivity is summarized in Fig. 9. The resistivity param- eters, E and RT, of the composite connected to Y-stabilized zirconia are comparable to those of the Y-stabilized zirconia alone. In addition, the activation energy of the bulk compo- nent was slightly lower than that of the grain component. It is concluded that the electrical properties are mainly con- trolled by the Y-stabilized zirconia layer, i.e. the conductivity of the composite layer is higher than that of the Y-stabilized zirconia layer. C0,-sensing Characteristics For the cell, expressed as: 02,Pt llNa ionic electrolyte INa2C03 IIPt, CO,, 0, 1.o 1.5 2.0 1O~WT Fig.9 Temperature dependence of the resistivity: Rbulk (a) and Rgrain (b) of the composite connected with Y-stabilized zirconia which was sintered at 1200 "C, and $?bulk (c) and Rgrain(d) of the Y-stabilized zirconia it is assumed that the chemical potential at the mode is controlled by the reaction: Na2CO,-,2Na+CO,+~O2 (9 whereas that at the cathode is represented by 2Na++02+Na20 (ii) The overall reaction is predicted to be Na,C0,-+Na20 +C02 (iii) When the oxygen concentration in the anode is kept the same as that in the cathode, the emf of the cell is expected to be = -(AGNazO +AGCO, -AGNa2C03)/2F -(RT/2F) In pCOz (2) where AGi is the standard Gibbs energy of formation and Pcoz the concentration of CO, in air.If the activity of Na20 remains constant, the emf gives the concentration of CO,. Fig. 10 shows the sensing characteristics at 470 "C for a sensor having the structure: O,, PtlZrO, llNa ionic electrolyte INa,C03 )IPt,C02,0,(iv) in which the composite connected to Y-stabilized xirconia calcined at 1200 "C was used for the electrolyte body. In this .. _.. . i -Ap.-. .-:-: , . lo , . . > 400-.. E .. 100== 7~ . _. ,-..-_.. .-...... . . ....s .... .. .... . ... ...... 1000 i, . -.300--,._... . ..... . 150 min_ ....._ -. _ . ._ 200 10000 1 Fig. 10 C0,-sensing behaviour of a sensor with the structure6 (refer- ence) PtJZrO, // Na ionic electrolyte INa2C0, // Pt (sensing electrode).CO, concentrations in ppm are denoted in the figure Fig. 11 CO, concentration dependence of the emf of the sensor with the structure given in the caption to Fig. 10. (a) Dry test gas and air in the reference, (b) dry test gas and 1OOOppm C02 gas in the reference, (c) wet test gas (dew point 30 "C) and air in the reference case, air (50ml min-') was introduced on the reference electrode side. On switching from 1000 ppm C0,-air flow to 100 ppm C0,-air flow, the emf increased rapidly and a steady- state value was observed. The rise and recovery times were very fast: the 90% response time was <2 min. When the CO, concentration was changed from 10000 ppm to 100ppm, from 100ppm to 10ppm and from 10ppm to air, the response time became longer.It seems that the concentration in the measuring cell could not be obtained soon after changing from a higher to a lower concentration. The response time was reduced by increasing the flow rate of the test gases and by increasing the number of measuring cycles. The con-centration dependence of the emf is shown in Fig. 11. A good linear relationship was confirmed and expressed by the relation, E/mV =514-72.5 log [Cco, (ppm)] in the range 10-10 000 ppm CO,. The sensitivity, 72.5 mV, is in reasonable agreement with the theoretical value, 74mV, based on eqn. (iii). In addition, when the air with 1000ppm CO, was introduced on the reference electrode side, the emf was expressed as: E/mV =5 15 -72.0 log [Cco2]in the same range.It is clear that the sensing characteristics are barely influenced by the C02 content on the reference electrode side. It is concluded that the activity of Na20 in the reference side/the interface of composite-Y-stabilized zirconia remains constant and is uninfluenced by changes in the concentration of C02 when the electrolyte is completely covered with Y-stabilized zirconia. The results suggest the possibility of fabricating a CO, gas sensor for use in ambient air without a control on J. MATER. CHEM., 1994, VOL. 4 the reference side. For a sensor expressed as: O,, Pt llNa ionic electrolyte)Na,CO, IIPt, CO,, 0, (v) in which the composite sintered at 1050 "C was used as the sodium-ion electrolyte, the emf in dry air is expressed as E/mV= 551 -74.5 log[Cco2] in the range 100-10000 ppm CO, when dry air is introduced to the reference electrode side.In this case, the sensitivity, 74.5 mV, is reasonably close to the theoretical value based on the two-electron electro- chemical reaction. When a test gas containing 10ppm CO, was used, the emf was lower than the extrapolated value estimated from the relationship confirmed at higher concen- tration ranges. Ambient air contains some water molecules, so the influence of humidity in the test gas on the sensing char- acteristics was examined. The result is shown in Fig. 11. When humid test air (30 "C dew point) was passed, the emf was lower than that measured for the dry test air, and in the range 100-10000ppm CO,, the emf is expressed as E/mV =496 -70.0 log[CCo2].Furthermore, the emf for [CO,] <100 ppm was lower than the value expected from the relation obtained in the higher range, the emf decrement increasing with decreasing CO, concentration. These dec- rements are ascribed to the formation of sodium oxides, such as Na,O and Na202, in the Na2C0, layer and/or the Pt electrode/body interface, as reported previ~usly.~~~," For the examined cell/sensor, the sensing characteristics in dry air remained almost constant even after exposure to humid air for 12 h or more. Furthermore, it is confirmed that the CO, concentration even in humid air can be measured without any distinct drift and/or loss of sensitivity (no distinct change in sensitivity was observed when sensing was carried out in humid air for 1 day or more). References 1 C. H. Kim, B. Qiu and E. Banks, J. Electrochem. SOL'., 1985, 132,1340. 2 E. Banks and C.H. Kim, J. Electrochem. Soc., 1985,132,2617. 3 K. Jackowska and A. R. West, J. Mater. Sci.,1983,18,2380. 4 D. Bahadur, Phys. Status Solidi (a), 1986,98, K23. 5 Y. Sadaoka, M. Matsuguchi and Y. Sakai, J. Mater. Sci., 1989, 24, 1299. 6 Y. Sadaoka, Y. Sakai and T. Manabe, J. Mater. Chem., 1992, 2,945. 7 Y. Sadaoka, Y. Sakai, M. Matsumoto and T. Manabe, J. Mater. Sci., 1992,28, 5783. 8 C.C.Hunter and M. D. Ingram, Solid State Ionics, 1984,14,31. 9 R. M. Hakim and D. R. Uhlmann, Phys. Chm. Glasses, 1971, 12, 132. 10 N. Matsui, Dennki Kagaku, 199 1,59,79 1. 11 J. Liu and W. Weppner, Eur. J. Solid State Inorg. Chem., 1991, 28, 1151. Paper 3/07424B; Received 17th December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400663
出版商:RSC
年代:1994
数据来源: RSC
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Influence of methane on the nitriding gas reduction of kaolinite |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 669-673
Alain Seron,
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摘要:
J. MATER. CHEM., 1994.4( 5), 669-673 Influence of Methane on the Nitriding Gas Reduction of Kaolinite Alain Seron,a Jacques Thebaulf‘ and Franqois Beguin” a CRMD, UMR CNRS Universite, 16 rue de la Ferollerie, 45071 Orleans cedex 2, France SEP, les cinq chemins, le Haillan, BP 37, 33165 St Medard en Jalles, France A new synthesis of P’-SiAION via the reduction and nitridation of aluminosilicates in the presence of a carbon source by a hydrogen-nitrogen gas mixture is presented. The formation of p-SiAION on surfaces (Sic, alumina) devoid of carbon was found to be impossible. Thermogravimetric analysis and mass spectrometry showed that, in a carbon crucible, methane was formed from the reaction of hydrogen with carbon. p-SiAION was obtained in the absence of free carbon by adding a small amount of methane to the hydrogen-nitrogen gaseous mixture.The formation of P’-SiAION is thus the consequence of reduction by methane rather than by hydrogen. Parasitic reactions of hydrogen lead to silicon elimination as SiO in the gas phase, and to a Si/AI ratio lower than in the starting kaolinite. Oxide ceramics have undergone important developments for centuries. Traditional ceramics have been used to make pot- tery, glass, bricks or cement which play an important role in everyday life. New oxide ceramics have been developed for many applications, but non-oxide ceramics are now widely used in specific cases. Of the non-oxide ceramics, carbides and nitrides are currently the most attractive. In addition, intermediates between oxide and non-oxide ceramics, new compounds such as oxycarbides and oxynitrides have now been developed.Our interest is in the synthesis of P‘-SiAlONs, which are silicon and aluminium oxynitrides.’ Compared with silicon nitride (P-Si3N4), from which they are derived, the main interest of these ceramics is their possibility of being densified. Indeed, obtaining dense materials from silicon nitride is impossible without additives such as A1203, MgO or Y203.’ Among the various preparation processes, p-SiAlONs can be formed from clay minerals at high temperature, using carbon as a solid reducer under a nitrogen atmosphere. Higgins and Hendry2 demonstrated that at least 4 h heating was necessary at 1400°C to obtain a significant amount of p-SiAlON.The powders obtained, after reaction, generally contain residual carbon which hinders sintering and prevents the formation of film coatings. On the other hand, even if obtaining P‘-SiAlON is easy, this compound is always synthe- sized together with by-products such as mullite or aluminium nitride.3,4 Such problems seem to be related to the inhomogen- eity of the solid-solid mixture even if some improvements can be obtained using carbon-oxide nanocomposites in which the reagents are highly di~persed.~.’ Better contact between the clay mineral and the reducing agent can be realized using a solid-gas reaction. In a previous paper: we described the synthesis of p-SiAlON using nitriding hydrogenoreduction of kaolinite in a nitrogen-hydrogen atmosphere, according to the theoretical equation (1) This is an easy method of producing P’-SiAlON at fairly low temperature (llOO°C), in a reasonable time (65 h).Even if 1450“C is the best temperature for carbored~ction,~ reaching such a temperature with hydrogen leads to products contain- ing a major portion of aluminium nitride which is the conse- quence of the reduction of P’-SiAlON. The thickness of the heat-treated samples strongly influences the nature of the products, owing to diffusion phenomena. Moreover, we found that the heat-treatment of aluminosilicates in alumina or silicon carbide crucibles under nitrogen-hydrogen flow ( 1:3) did not yield P’-SiAlON, as did the same treatment in carbon crucibles.Because gas reduction occurred at a very low temperature compared with carboreduction, we suggested the existence of a carbonaceous species in the gas phase6 These results seem to contradict those reported by Wild; who showed that a mixture of P’-SiAlON and A1N could be obtained by heating clay minerals in an alumina crucible under ammonia flow. This paper will demonstrate that carbon is absolutely necessary in the nitriding gas reduction process of kaolini te. Experimental The clay mineral used in this work for producing P-SiAlON was a kaolinite (‘kaolin supreme des Charentes’). The chemical composition given by elemental analysis was: Si 20.35%, A1 18.70%, Fe 0.40%0, Ca 0.10%, Mg 0.20%, Na 0.10%, K 0.85Y0,Ti 0.02%. In a typical experiment, a thin layer of kaolinite (200mg) was heat-treated in alumina, Sic or graph- ite crucibles under nitrogen-hydrogen (N2, 100cm.‘ min-’; HZ, 300 cm3 min-’, both gases from ‘Air Liquidc’: H20, 0,<5 ppm) at 1100 “C6 Tb 1450 “C, with a heating rate of 300°C h-’ and 0.5 to 100h at the highest temperature.We used a vertical tubular furnace with a sintered Al,03 tube (diameter 7 cm). The lower and upper parts of the Al,03 tube were filled with cement cylinders. A 90cm3 free space was available in the centre of the tube to place the crucible containing the sample on the lower cylinder. The temperature of the specimen was determined by a Pt/PtRh 10% thermo-couple under the crucible. Before heating, the furnace was evacuated for 0.5 h to lO-’mbar and then swept by the nitrogen-hydrogen mixture.The synthesized products wer? characterized by powder X-ray diffraction at 3, =1 S405A (Siemens D 500 goniometer) in a reflection set-up. Thermal treatments were also carried out in a thermo-gravimetric analysis (TG) apparatus coupled with a mass spectrometer.8 Such a set-up enables the analyses of the components in the outflowing gases and allowed us identify the different steps of the reaction. For the other experiments, we used a furnace with a vertical A1203 tube. For these analyses, the aluminosilicate powder (ca. 20 mg) was In either alumina or carbon crucibles. The thermobalance wa:, evacu- ated (P=lo-’ mbar) before heat-treatment, then swept by nitrogen-hydrogen flow (1 :3).The temperature of the samples was determined, by a Pt/Pt Rh 10% thermocouple under the 670 crucible and the mass was determined by an electromagnetic balance (10-8 MTB Setaram). Evolved gases were sampled by a heated alumina capillary set just near the crucible and continuously analysed by a mass spectrometer (Balzers QMG 420 C), from which selected masses were plotted as a function of time, i.e. of sample temperature. Results and Discussion When kaolinite was heat-treated in alumina or silicon carbide crucibles, under nitrogen-hydrogen flow (1 :3), only mullite and cristobalite were formed (Fig. l).' We obtained the same phases in the presence of ammonia, contrary to the results reported by Wild.7 Indeed, these authors reported that a mixture of P'-SiAlON and AlN could be obtained by heating clay minerals in an alumina crucible under ammonia flow, and they do not mention the existence of carbon in their experimental set-up.On the other hand, we observed that heat-treatment of kaolinite in carbon crucibles under N,-H, flow led to the formation of /l'-SiAlON after 3 h heating at 1350°C [Fig. 2(b)].Apparently, the presence of carbon near the clay sample is necessary for the production of /l'-SiAlON. After heat-treatment of clay mineral samples in carbon crucibles under N,-H,, scanning electron microscopy showed that the carbon support was corroded near the oxinitride powder (Fig. 3). This was at first attributed to a carboreduction I I 12 ' 16 ' 20 24 28 32 36 40 2#degrees Fig.1 X-Ray diffractogram of the solid phase obtained after thermal treatment of kaolinite at 1200°C (48 h plateay) in an alumina crucible H,-N, =3 : 1, 400 cm3 min-'; (A = 1.5405 A); 0=cristobalite, H =mullite I' , . . . . '+ ' ,.... 'I 1, I,,,,,12 ' 16 20 24 28 32 36 40 2BJdegrees Fig. 2 X-Ray diffractograms of the solid phases obtained after 3 h heat-treatment of kaolinite at 1350 "C. (a) nitrogen, 100 cm3 min-'; =cristobalite, H =mullite. (b) Nitrogen-hydrogeq, H,-N, =3 :1, 100 cm3 min-'; *=P'-SiAlON, 0 =AlN (A= 1.5405 A). J. MATER. CHEM., 1994, VOL. 4 Fig.3 Corrosion of a carbon crucible (arrows) after the nitriding hydrogenoreduction of kaolinite, as seen by scanning electron microscopy phenomenon allowing the formation of P'-SiA10N,3 but this hypothesis was contradicted by the result of heating pure kaolinite in a graphite crucible at 1350 "C under nitrogen.Under these conditions, and even after 3 h heating, neither AIN nor P'-SiAlON was formed [Fig. 2(u)]. The only phases detected were mullite and cristobalite, whereas /i'-SiAlON and A1N were easily synthesized in a nitrogen-hydrogen flow. Slight carboreduction could only be observed after 48 h heating in a graphite crucible at 1450"C, whereas P'-SiAlON was totally reduced into A1N after only 10 h under N2-H2 flow. It is therefore likely that P'-SiAlON is not formed by a carbothermal process through a solid-solid interaction between the clay mineral and the carbon support.To demon-strate the influence of a gas formed from the carbon support, a kaolinite sample in an alumina crucible was put on a graphite plate, surrounded by a graphite cylinder, and heated under nitrogen-hydrogen (Fig. 4). Under these conditions, p'-SiAlON with a small quantity of mullite were obtained after heating at 1350°C for 3 h [Fig. 5(b)].On the contrary, when the alumina crucible was only put on the carbon plate without any graphite cylinder, the major phase obtained was mullite [Fig. 5(u)]. Another proof that a gaseous carbon species could influence the reduction process was given by the reaction of silica under N,-H2 flow in an alumina crucible surrounded by a graphite cylinder (Fig. 4). The only phase detected (Fig.6) was silicon carbide, showing that a sufficient amount of a carbonaceous species was carried by the gaseous phase to reduce all the powder. Indeed, Shickg and Lee and Cutler"' showed that carbon could reduce silica in this temperature range and convert it to silicon carbide. We therefore propose for the reduction of SiO,: SiO, +3C(g)+Sic +2CO (2) Fig. 4 Experimental set-up design to clarify the role of carbon J. MATER. CHEM., 1994, VOL. 4 671 ~ , , . . , .,..., ...,...,.. , .,, , .., ,.. , ,.J I.. ..,. ,,.. ,.. , .,,...,...,...,., /.. .,. ,,..., ..,,.., ../,I12 16 20 24 28 32 36 40 2Wdegrees Fig. 5 X-Ray diffractograms of the solid phases obtained after 3 h heat-treatment of kaolinite at 1350'C in an alumina crucible (u) without graphite cylinder, W =mullite, *=p-SiAlON; (b) with graphite cylinder, Hz-N2=3 :1; 400 cm3 mi;-';W =mullite, *=p'-SiAlON, +=Al,O,N, W =AlN; (3.=1.5405 A) 1Ii iI i i ~ I 12 16 20 24 28 32 36 40 2Hdegrees Fig. 6 X-Ray diffractogram of the solid phase obtained after thermal treatment of silica surrounded by a graphite cylinder Jplateau at 1200"C, 48 h); Hz:Nz=3 :1, 400 cm3 min-'; (i=1.5405A); V=Sic where C(g) represents a carbon-bearing gaseous species. To confirm this hypothesis we built an apparatus consisting of a thermogravimetric (TG) analysis apparatus and a mass spec-trometer, thus giving us simultaneously the mass loss and the molecular mass of the evolved gases (m/z us. time). It was shown previously that when kaolinite is heat-treated in an alumina crucible under neutral atmosphere (N,, Ar), only one mass loss is observed, close to 500°C.6 The XRD analysis of the resulting powder indicated that it contained non-reduced phases: mullite and cristobalite.The mass loss observed by TG was confirmed by mass spectrometry, which showed peaks at m/z= 17 (OH') and m/z= 18 (H,Of) cor-responding to the dehydroxylation of kaolinite. A similar heat-treatment of a kaolinite sample in a graphite crucible led to two mass losses at 500 and 1100"C,respectively (Fig. 7). The first is attributed to the loss of hydroxy groups whereas the second, which reaches 74% in mass after a 1 h plateau at 1350"C,seems to be due to the reduction of a part of silica by the carbon substrate'' generating the loss of silicon as SiO and carbon as CO: SiO, +C+ SiO +CO (3) The SiO loss is confirmed by the X-ray diffraction spectrum of the powder obtained, which only contains a small amount of silica as cristobalite (Fig.8) compared to the one heat-treated in the same conditions in an alumina crucible (Fig. 1). On the other hand, mass spectrometry of the gas evolved (Fig. 9) showed a loss of carbon monoxide and carbon dioxide, isotherm I I 11 I 250 500 750 1000 1250 1360 V0C Fig. 7 Thermogravimetric analysis of kaolinite in a graphite crucible under nitrogen flow; heating rate 200°C h-l, plateau at 1350°C; 1 h, DN2=100 cm3 min -II II 'I2 ' 16 ' 20 ' 24 28 ' 32 ' 36 ' 4'0 28Jdegrees Fig.8 X-Ray diffractogram of the solid phase obtaincd after thermal treatment of kaolinite at 1350"C (1 h plateau) in a graphite crucible under nitrogen flow: N,, 100 cm3 min-'; (A= 1 5405 A); =cristobalite, W =mullite .12I I '\II i I I I----------i i I 1 I I I,,isotherm 250 750 125011350 T/"C Fig.9 Mass spectrometry (m/z us. TIT) of the gas generated by the heat treatment of kaolinite in a graphite crucible under nitrogen flow. Same experimental parameters as in Fig. 8 characterized by peaks at m/z= 12 (C') and m/z=44 (CO;) and confirmed by m/z= 16 corresponding to the 0' ion. The existence of these gases must be attributed to the zlassical reaction which favours C02 at low temperature and CO at high temperature (>1000OC): 2CO+-CO,+C (4) 672 The characteristic ion for CO (m/z =28) could not be detected because of the presence of a large amount of nitrogen in the atmosphere, nor could silicon monoxide be detected by mass spectrometry because of its condensation in the cold part of the apparatus.B'-SiAlON was readily obtained by heat-treatment of kao- linite under H,-N, flow in the graphite crucible of the TG apparatus. The TG curves showed two mass losses, in the range 300-600°C (elimination of hydroxy groups) and in the range 1000 to 1350°C (Fig. 10).The last mass loss is almost independent of the initial mass of clay mineral but only influenced by the residence time at 1350 "C. Mass spectrometry (Fig. 11) points to the formation of a small amount of ammonia close to 800°C [NH,' (m/z=17), NH,f (rn/z=16), NH' (m/z = 15)and N+ (m/z = 14)], because these peaks were non-existent when the treatment was performed under a hydrogen-argon flow.Above 1000 "C, symmetric peaks for C' (m/z=12), CH' (m/z= 13), CH,f (m/z=14), CH,' (m/z= 15) and CH,f (rn/z=16), all corresponding to methane, appeared. As expected from the equilibrium constant K, [corresponding to eqn. (5)] the formation of this gas reaches 1.0. F"Ed -isotherm 1350 I I I I I , , I I I I 250 750 1250 1250 750 TI0C Fig. 10 Thermogravimetric analysis during heat-treatment of kaolin- ite under nitrogen-hydrogen flow in a graphite crucible; heating rate 200°C h-', plateau at 1350°C, 1 h, H,:N,=3:1,400cm3 min-' 500 1000 1000 500 TI"C Fig.11 Mass spectrometry of the gas generated by the heat treatment of kaolinite in a graphite crucible under nitrogen-hydrogen flow. Same experimental parameters as in Fig. 8 J. MATER. CHEM., 1994, VOL. 4 a maximum rate at a temperature close to llOO°C, whereas increasing the temperature above 1100"C lowers its partial pressure, which becomes stable during the isothermal plateau. Besides the signal corresponding to C+ (m]:= 12), another gas is detected during the isothermal plateau which seems to be CO. It is likely that hydrogen is not directly responsible for the formation of p-SiAlON, but that it rather reacts with the carbon support to form methane [eqn.(5)]which then reduces kaolinite [eqn. (6)]: C +2H, + CH, (5) 3 (A1,03,2Si02)+ 15CH, + 5N, +2Si3Al3 O3N, + 15CO+30H2 (6) In equilibrium (5), the partial pressure of CH, at 12OOcC, deduced from K, (Kp=3.16 x is 300 Pa. By mixing 74.78% hydrogen, 0.22% methane and 25% nitrogen, a mixture with the same partial pressure of CH4 was prepared, which was then allowed to react with kaolinite in alumina crucibles at 1200°C for 48 h. Fig. 12 shows that, under these conditions, almost pure /3'-SiAlON was formed. Because all the experimental data are the same as in Fig. 1, except the small amount of methane incorporated in the vapour phase, this experiment clearly demonstrates that methane is respon- sible for the nitriding reduction of kaolinite.We tried to increase the methane content of the gaseous mixture. For instance, heat-treatment of kaolinite under a flow of nitrogen (100cm3 min-I), hydrogen (300 cm3 min-l) and methane (10 cm3 min-') at 1200"C for 48 h did not yield B'-SiAlON because of the formation of a carbon film on the surface of the sample: the partial pressure of methane was higher than the equilibrium value, and a part was dissociated, accordingly to eqn. (5). Thus, even if methane is solely responsible for P'-SiAlON formation, hydrogen is necessary to avoid the dissociation of the methane. Even if eqn. (6) is fairly representative of B'-SiAlON forma- tion by the gas reduction of kaolinite, it is likely that the real process is more complicated because of side-reactions such as the reduction of silica by hydrogen according to: Si02+H, +SiO +H20 (7) This reaction certainly occurs, because we always synthesized B'-SiAlON with Si :A1 < 1 (Table 1), the theoretical value which should be obtained if only methane reduction occurred Ceqn.To describe the formation of P'-SiAlON from the reaction 12 16 20 24 28 32 36 2Bldegrees Fig.12 X-Ray diffractogram of the solid phase obtained after nitriding reduction of kaolinite in an alumina crucible under hydrogen-nitrogen-methane flow with a plateau at 1200"C (48 h): HZ,?4.78%; N,, 25%; CH,, 0.22%; Dtota,=400 cm3 min-'; (A=1.5405 A); *=/?'-SiAlON, =mullite J. MATER. CHEM., 1994, VOL. 4 Table 1 Si: A1 ratios given by elemental analysis of kaolinite and of samples obtained after nitriding gas reduction of kaolinite on graphite crucibles samplea experimental parameters Si : A1 kaolinite -1.05 H2:N,=3: 1 1 plateau at 1450 “C (10 h) 0.11 H2:N2=3:1 2 plateau at 1350°C (3 h) 0.87 “Sample 1 was identified as p-SiAlON whereas sample 2 is essentially AlN by X-ray diffraction.between kaolinite and ammonia, Wild proposed a reaction scheme very similar to eqn. (l),which does not involve any carbonaceous species. In fact, he described in detail neither the experimental set-up used nor the purity of the ammonia in term of ‘carbon’ traces. Our results suggest that this author was able to obtain p’-SiAlON owing to the presence of unidentified methane, either already existing in ammonia, or formed from the reaction of ammonia with any carbon substrate.Conclusions The synthesis of p’-SiAlON by heat-treatment of kaolinite under hydrogen-nitrogen flow is impossible without a carbon source. Using graphite crucibles, the analysis by mass spec- trometry of the gas evolved showed the formation of methane which acted in the formation of p-SiAlON. Pure P’-SiAlON could be obtained by heat-treatment of kaolinite in alumina crucibles under nitrogen-hydrogen-methane ternary mixture, without another source of carbon. The use a nitrogen-methane gas mixture is, however, impossible because its results in the formation of carbon coating on the surface of the samples which inhibits the reduction. The main reaction generating p’-SiAlON from kaolin is the methane nitriding reduction.However, side-reactions such as the elimination of SiO by hydrogen reduction cannot be rejected. This treatment of kaolinite, at relatively mild temperatures, by the hydrogen- nitrogen-methane mixture, allows the formation of thin films with low porosity at the surface of a carbon substrate. This process could be applicable for the ceramic coatings of carbon materials. Thanks are due to the ‘Societe Europeenne de Propulsion’ for financial support. References 1 K. H. Jack, J. Muter. Sci.,1976, 11, 1135. 2 I. Higgins and A. Hendry, Br. Ceram. Trans. J., 1986,85, 161. 3 J. B. Baldo, V. G. Pandofelli and J. R. Casarini, Ceram. Powd., ed. P. Vincenzini, Elsevier, Amsterdam, 1983, pp. 437. 4 Y. Sugahara, J. Mitamoto, K. Kuroda and C. Kato, Appl. Clay Sci.,1989, 4, 11. 5 A. Seron, I. Ben Maimoun, M. Crespin and F. Beguin, Marer. Sci. Eng., 1993, A168,239. 6 A. Seron, J. Thebault and F. Beguin, J.Muter. Res., in the press. 7 S. Wild, J. Muter. Sci., 1976,11, 1972. 8 A. Seron, PhD Thesis, 1993, Orleans. 9 H. L. Shick, Chem. Rev., 1960,60,331. 10 J. G. Lee and I. B. Cutler, Ceram. Bull., 1975,54, 195. 11 P. D. Miller, J. G. Lee and I. B. Cutler, J. Am. Ceram. So( ., 1978, 62. 147. Paper 3/07414E; Received 16th December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400669
出版商:RSC
年代:1994
数据来源: RSC
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Electroluminescence of organic thin films based on blends of polystyrene and fluorescent dyes |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 675-678
Peter Frederiksen,
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摘要:
J. MATER. CHEM., 1994,4(5), 675-678 Electroluminescence of Organic Thin Films based on Blends of Polystyrene and Fluorescent Dyes Peter Frederiksen, Thomas Bjarnholm,* Hans Georg Madsen and Klaus Bechgaardt Centre for Interdisciplinary Studies of Molecular Interactions, Department of Chemistry-Symbion, University of Copenhagen, Fruebjergvej 3, DK-2 700 Copenhagen 0,Denmark Blue and red light-emitting diodes were constructed as devices in which a polystyrene/dye blend was sandwiched between a calcium electrode and a transparent indium-tin oxide electrode. As dye molecules, four alkoxy-substituted derivatives of 2,5-dialkoxy-l,4-bis(2-phenylvinyl)benzene (inemp-phenylene vinylene oligomers), a derivative of bisanthra- cene (2,2’,3,3’-tetrachloro-9,9’-dimethoxy-l0,1O’-bianthracene) and the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminophenylvinyl)-4H-pyran (DCM) were used.The critical field for light emission in devices using 20 wt.% PPV oligomers in polystyrene was found to be of the order of 2 x 1O8 V m-’. The dependence of the device conductivity on the concentration of dye molecules in the polystyrene film is described by simple percolation theory. The synthesis of 2,2’,3,3’-tetrachloro-9,9’-dimethoxy-l0,1O’-bianthracene is reported. In recent years two new types of light-emitting diode (LED) have been reported. One type uses thin molecular films of simple fluorescent molecules as the light-emitting layer,’-5 the other type uses conjugated polymers, e.g. poly(p-phenylene vinylene) (PPV) as the active polymer in thin-film based devices.&14 In both cases, electrons injected at the negative electrode and holes injected at the positive electrode recombine in the organic thin film, forming excited states which decay radiatively.The present paper is concerned with an intermediate situ- ation in which a blend containing a fluorescent PPV oligomer, or other fluorescent molecules in a neutral host polymer, e.g. polystyrene, forms the electroactive layer. Such films have recently been demonstrated to be electroluminescent.’5~16We present here investigations describing the dependence of the electroluminescence on the type of fluorescent molecule, the loading of the fluorescent molecules in the host polymer film and the nature of the polymer host.The results show that well dispersed blends of the fluorescent guest molecules in polystyrene form efficient light-emitting diodes compared to diodes using saturated polymer hosts like poly(methy1 meth- acrylate). The colour of the diode is readily changed by changing the guest molecules. Experimental The PPV oligomer dyes (Fig. 1) were synthesized by a Horner-Emmons variation of the Wittig reaction, between a suitable p-xylylene diphosphonate and a suitable benzal- dehyde, in a similar manner, as described in ref. 17 and 18. Mixtures of cis and trans isomers were analysed by HPLC, and the fraction of the all-trans isomer was found to be 50-100% (Table 1). of CH2C12, dried over MgSO, and filtered through ;ishort column of silica gel.The resulting solution was evaporated to dryness to yield 10.0 g (95%) of BA as a glass. To obtain crystals, the product was dissolved in CH,Cl, and precipitated by adding petroleum ether. Mp: 304-305°C.1 H NMR (60 MHz, CDCl,, standard TMS) 6: 4.3 (s, 6H); 6.8-7.7 (m, 8H); 8.3-8.7 (m, 4H). Calcd. for C3,H18C1,02: C. 65.24; H, 3.29; Cl, 25.68%. Found: C, 65.00; H, 3.37; C1, 26.00Y0. The laser dye, DCM, and the various polymers were commercially available. The molecular weight distribution of the polymers did not have a pronounced effect on the proper- ties of the diodes. LED devices were constructed by using an indium-tin oxide (ITO) coated glass substrate, where the IT0 glass serves as a transparent hole-injecting electrode.The glass/ITO substrates were cleaned by washing them with water and propan-2-01, and finally vapour, degreasing them in chlorobenzene. On this substrate a layer of the polystyrene/dye blend was formed by spin-coating a solution in chlorobenzene of the desired mixture of guest and host. On this film, a layer of calcium was vacuum deposited ( Torr) through a mask, to obtain round spots with areas of ca. 12mm2. Finally, a layer of aluminium was vacuum deposited on the calcium electrode to protect it from oxidation and corrosion. A typical film containing 20 wt.% of the dye and having a thickness of 150nm was obtained by spin-coating using a solution of 10mg of the dye, and 40mg of polystyrene in 1 ml of chlorobenzene. The thickness of the films was calculated using the molar absorption coefficient for dilute solutions and the measured absorbance at the absorption peak of the dye.$ The resulting thicknesses agreed with profile measurements and thicknesses obtained from analysis of the fringes resulting from optical measurements of the films.Synthesis of 2,2’,3,3’-tetrachloro-9,9’-dimethoxy-10,10’-bianthracene (BA): A slurry containing 2,2’,3,3’-tetra-chloro-10,lO’-bianthronyl(10.0 g, 19.9 mmol) (19), 1 ml of absolute ethanol and 200ml of dry DMF was prepared. Sodium hydride (1.26 g, 2.20 equiv., 80% in mineral oil) was added under nitrogen. A red homogeneous solution was formed as the bianthronyl dissolved. When no more gas evolved, dimethyl sulfate (4.0 ml, 2.2 equiv.) was added and the solution was stirred for 24 h.The yellow opaque solution containing the product was poured into 500 ml of water. The precipitate was filtered, washed with water, dissolved in 150 ml t Present address: Department of Physics, RIS0 National Laboratory, DK-4000 Roskilde, Denmark. The current-voltage characteristics were measured using a standard power supply and an X/Y recorder or with a standard digital voltmeter and amperemeter (Fig. 2). Light emission was analysed using a Perkin-Elmer LS 5 spectrometer. Results Electroluminescence was observed from devices based on polystyrene blends of the fluorescent guest molecules shown $d=103(AM,)/psw, where d is the film thickness in pnm, A is the absorbance of the film, M, is the molecular weight of the guest molecule, w is the weight percent of the guest in the host, E is the absorption coefficient measured in dilute solution (in dm3 mol-I cm-l) and p is the density of guest and host (in g cmP3).J. MATER. CHEM., 1994, VOL. 4 I I ,o P 0‘O’ I I PPVO1 PPVO2 I 01 I/. -\ \/ \ \I d \ \/\\Ilo--0 0 -0 -0 I /-O PPVO3 PPVO4 0’ 1 CI clyJ-pCI yo BA DCM polymer host molecules: CI polystyrene poly(rnethyi methacrylate) poly(viny1 chloride) Fig. 1 Guest and host molecules used in the investigation. Abbreviations as follows: PPVO 1, 2,5-dimethoxy- 1,4-bis( 2-phenylviny1)benzene; PPVO2, 1,Cbis[244-methoxyphenyl)vinyl]-2,5-dimethoxybenzene;PPVO3, 1,Chis[24 2,4-dimethoxyphenyl) vinyl]-2,5-dimethoxybenzene; PPVO4, 1,4-bis[2-(2,5-dimethoxyphenyl)vinyl]-2,5-diethoxybenzene; BA, 2,’3,3’-tetrachloro-9,9-dimethoxy-10,lO-bianthracene; DCM, 4-dicyanomethylene-2-methyl-6-( p-dimethylaminophenylvinyl)-4H-pyran Table 1 Electroluminescence from devices based on polystyrene blends of fluorescent guest molecules of Fig.1 Amax (electroluminescence)/ €1 guest nm lo4dm3 mol-’ cm-’ PPVOl 484 388 2.7 PPVO2 482 394 4.6 PPVO3 494 398 4.4 PPVO4 461 402 BA“ 458 27 1 7.6 DCM 620 472 4.2 “The transition with lowest energy appears at 11=415 nm (E= 1.8 x lo4dm3 mol-’ cm-I). Ratio of cisltrans isomers (based on HPLC measurements): PPVOl and PPVO2 100% trans-trans; PPVO3: trans-trans 72%; cis-trans 28%. PPVO4: trans-trans 48%, cis-trans 33YO; cis-cis 19%.in Fig. 1 (Table 1). Different batches of polystyrene were used All electroluminescent devices exhibit an electroluminesc- with no pronounced effect on the quality of the devices. Under ence spectrum which is very similar to the photoluminescence the same experimental conditions high-quality films of the spectrum of the same films (see Fig. 3 as a representa-dyes could be produced using PMMA and PVC as the host tive example). Since the excitation spectrum of the films polymer, but electroluminescence could not be observed from additionally resembles the absorption spectrum of the guest devices based on these films. molecules (Fig. 3), it is evident that the electroluminescence J. MATER. CHEM., 1994, VOL.4 I calcium II Fig. 2 Schematic illustration of the device configuration I --1 350 400 450 500 550 600 wavelengthhm Fig.3 Optical properties of a film of PPVO3 in polystyrene. (-) Absorption spectrum, (---) excitation spectrum, electroluminescence spectrum (EL) and photoluminescence spectrum (PL) of the film. The dashed thin line shows the absorption spectrum of a dilute solution of PPVO3 in CH,Cl,. The properties are representative of the films investigated. occurs by radiative decay of an electronically excited guest molecule. The absorption spectrum of the guest molecules densely packed in the polymer films (20wt.%) resembles the spec- trum of dilute solutions of the guest molecules (Fig. 3). Measurements of the dichroic ratio at normal incidence and skew angles of incidence2' of some of the samples revealed a highly isotropic distribution of the guest molecules in the polymer films.Comparison of the absorption at Laxof dilute solutions in 1 cm cuvettes and films of known thicknesses revealed that within a 10% margin, the molar absorption coefficient of the guests in the films was identical to the absorption coefficient in dilute solution (Table 1). These results are all indicative of a molecularly dispersed mixture of guest and host. In the following we therefore assume that no strongly bound aggregates of the molecules are formed. The current-voltage characteristics of a representative device show diode behaviour, allowing a current to run through the device when the Ca electrode is negatively biased above a certain critical value, but not vice versa.The onset of light emission occurs at slightly higher bias voltages, as shown by the inset in Fig.4.With a 50 mA current running through the device at ambient conditions, the half-life was 90 min. The LEDs were stable for weeks when they were kept under dry argon and zero current. The p-phenylene vinylene oligomer (PPVO) based diodes were the most stable of the devices studied here. Investigations of samples of different thicknesses of PPVO3 2.0 1.5 2 1.0 2 0.5 bias voltageN I0 0.0 -0.5 Fig. 4 Current-voltage characteristics of a device using 20 wt.% PPVO3 in polystyrene. Inset: (-), current; (---), luminescence reveal a linear dependence of the driving voltage on the film thickness (Fig.5). From the slope of the plot in Fig. 5 the critical field for light emission is estimated to be 1.7 x lo8V m-'. The dependence of the current-voltage characteristics on the loading of guest in the host polymer is shown in Fig. 6. At zero loading the diode characteristics are absent and it is not possible to drive a current through the device using voltages below the critical voltage for dielectric breakdown. The clear signature of the diode characteristics occurs at loadings higher than ca.10wt.%. The same data are replotted in Fig. 7 to show the dependence of the current on the loading at constant bias voltage. A steep rise in the current appeared at ca. 15 wt.% of guest molecules.This behavior is typical of percolation behaviour as discussed further in ref. 21. I 1 0 100 200 300 400 500 600 film thicknesshm Fig.5 Drive voltage us. film thickness of devices using 20wt.% PPVO4 in polystyrene. Slope = 1.72 x lo8V cm-l 1200 20%:Innrr I/15% 2001 0-0% I I 1 I I J. MATER. CHEM., 1994, VOL. 4 PVC since the latter does not contain an appreciable 7c-electron density. The mean molecul$r separation at the onset of the rise in Y 2 150 I? 4001 I I0 4 8 12 16 20 IE 300-d/B, I I 30 2001 I I I I I I 100-------*-- - - -4 I L weight (%) Fig. 7 Current us. wt.% at constant bias voltage (32 V) for PPVO3 in polystyrene (the inset shows the dependence of the current on the mean molecular separation of the dye molecules in the polymer) Discussion LEDs of a number of blends of fluorescent molecules and polystyrene have been constructed and investigated.The electronic properties of the fluorescent molecule govern the colour of the device (Fig. 3) and the miscibility of the guest molecules in polystyrene governs the quality and efficiency (Fig. 7). Our results indicate that it is possible to create a large variety of colours by using these types of device. The luminescence of the device resembles the fluorescence of the dye (Fig. 3). The clear evidence of a critical field for light emission (Fig. 5) indicates that the diodes are tunnel diodes” and not Schottky diodes. The quantum efficiency of the devices has not been measured, but the dependence of the current (and luminescence) on the amount of guest in the host polymer (Fig.6) shows that optimization of the loading can improve the efficiency of the device considerably. Reasonable efficiencies have been reported for similar system^.'^ At constant electric fields the conductivity behaviour (i.e. current-voltage) shown in Fig. 7 clearly resembles the behav- iour of systems of metal-insulator blends described by per- colation theory.21 In three dimensions the critical volume fraction for conductivity in such systems is 16%21 and, assuming that the densities of guest and host in our systems are similar; this corresponds to a critical amount of 16 wt.%. As seen from Fig. 7, the agreement with this value is remark- able, indicating that percolation phenomena govern the con- ductivity of the devices. The resemblance between the photoluminescence and the electroluminescence in the films shows that localized exci- tations of dye molecules are important.The dependence of the device conductivity on loading shows that conduction is mediated by the guest molecules, and that the intrinsic conduc- tivity of the polymer host is very low (Fig. 6). It is therefore plausible to assume that the mechanism for conductivity occurs by electron or hole hopping from dye molecule to dye molecule. In this context the polymer host plays the role of a tunnelling barrier. Since efficient devices could only be made using the polymer with a relatively high n-electron density it is plausible that tunnelling from guest to guest is the mechan- ism of conduction because n-electrons in the polymer barrier between guests (as in polystyrene) offers lower-lying states than in the corresponding saturated polymers. Polystyrene will hence act as a lower energy barrier than PMMA and conductivity is ca.8 A as seen from the inset in Fig. 7. Since this separation represents an upper limit for the separations found in the possible percolation cluster responsible for con- ductivity, mean molecular separations are indeed small enough to allow significant tunnelling probabilities for the hopping process from guest to guest. We wish to thank K. Schaumburg Ib Johannsen and Ole Kramer for useful discussions and the Danish Materials Research Program for funding.References 1 C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987,5,913. 2 C. W. Tang, S. A. VanSlyke and C. H. Chen, J. Appl. Phys., 1989, 65, 3610. 3 C. Adachi, T. Tsutsui and S. Saito, Appl. Phys. Lett., 1989, 55, 1489. 4 C. Adachi, T. Tsutsui and S. Saito, Appl. Phys. Lett., 1990,56,799. 5 C. Adachi, T. Tsutsui and S. Saito. Appl. Phys. Lett., 1990,57,531. 6 J. H. Burroughs, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature (London), 1990,347,539. 7 D. Braun and A. J. Heeger, Appl. Phys. Lett., 1991,58,1982. 8 D. D. C. Bradley, A. R. Brown, P. L. Burn, J. H. Burroughes, R. H. Friend, A. B. Holmes, K. D.Mackay and R. N. Marks, Synth. Met., 1991,41-43,3135. 9 A. R. Brown, N. C. Greenham, J. H. Burroughes, D. D. C. Bradley, R. H. Friend, P. L. Burn, A. Kraft and A. B. Holmes, Chem. Phys. Lett., 1992,46,200. 10 P. L. Burn, A. B. Holmes, A. Kraft, D. D. C. Bradley, A. R. Brown, R. H. Friend and R. W. Gymer, Nature (London), 1992,47,356. 11 G. Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri and A. J. Heegei, Nature (London), 1992,357,477. 12 R. H. Friend, D. D. C. Bradley and A. B. Holmes, Phys. World, Nov. 1992, 42. 13 D. D. C. Bradley, Adu. Muter., 1992,4,756. 14 D. A. Halliday, P. L. Burn, D. D. C. Bradley, R. H. Friend, 0. M. Gelsen, A. B. Holmes, A. Kraft, J. H. F. Martens and K. Pichler, Adu. Muter., 1993,5,40. 15 See W.Tachelet and H. J. Geise, Abstract book, ICSM’92, Gothenburg, Sweden, 1992; W. Tachelet, H. J. Geise and J. Gruner, to be published. 16 H. Vestweber, J. Oberski, A. Greiner, W. Heitz, R. F. Mahrt, H. Bassler, Adu. Muter. Opt. Electron 1993, 2, 197; H. Vestweber, A. Greiner, U. Lemmer, R. F. Mahrt, R. Richert, W. Heitz and H. Bassler, Adu. Muter., 1992,4,661. 17 Z. Yang, H. J. Geise, M. Mehbod, G. Debrue, J. W. Visser, E. J. Sonneveld, L. Van’t dack and R. Gijbels, Synth. Met., 1990, 39, 137. J. Nouwen, D. Vanderzande, H. Martens, J. Gelan, Z. Yang and H. J. Geise, Synth. Met., 1992,46,23. 18 S. Jacobs, W. Eevers, G. Verreyt, H. J. Greise, A. De Groot and R. Domisse, Synth. Met., in the press. 19 E. Barnett, Berichte 1932,65B, 1563. 20 J. Michl, E. W. Thulstrup, Spectroscopy with Polarised Light, VCH, Weinheim, 1986; T. Bjerrnholm, N. B. Larsen, F. E. Christensen, P. Sommer-Larsen, T. Skettrup and M. Jnrrgensen, Synth. Met., 1993,57, 3813. 21 D. J. Phelps and C. P. Flynn, Phys. Rev. B, 1976, 14, 5279; R. Zallen, The Physics of Amorphous Solids, John Wiley, Chichester, 1983,4, p. 187. 22 I. D. Parker, J. Appl. Phys., submitted. 23 W. Tachelet, H. J. Geise and J. Gruner, personal communication. 24 See eg., Metal Ions in Biological Systems, ed. H. Sigel and A. Sigel Marcel Dekker, New York, 1991, vol.27; R. R. Dogonadze, Reactions of Molecules at Electrodes, ed. N. S. Hush, John Wiley, Chichester, 1971,p. 135. Paper 3/07313K; Received 10th December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400675
出版商:RSC
年代:1994
数据来源: RSC
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1,3-Disubstituted ferrocene-containing thermotropic liquid crystals of form (η5-C5H5)Fe[(η5-C5H3)-1,3-(CO2C6H4CO2C6H4OCnH2n+1)2] |
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Journal of Materials Chemistry,
Volume 4,
Issue 5,
1994,
Page 679-682
Robert Deschenaux,
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摘要:
J. MATER. CHEM., 1994, 4(5), 679-682 1,3=Disubstituted Ferrocene-containing Thermotropic Liquid Robert Deschenaux,*a Julio Santiago: Daniel Guillonb and Benoit Heinrichb a Universite de Neuchitel, lnstitut de Chimie, Av. de Bellevaux 51, 2000 Neuchiitel, Switzerland lnstitut de Physique et Chimie des Materiaux de Strasbourg, Groupe des Materiaux Organiques, 67 rue du Loess, 67037 Strasbourg Cedex, France The title compounds have been synthesized and their liquid-crystal properties investigated. The reported ferrocene derivatives exhibited enantiotropic nematic and/or smectic A phases associated with broad anisotropic domains. The molecular arrangement within the smectic A phases was studied by X-ray diffraction. The experimental data, compared to the values obtained from CPK models, suggested a monolayer molecular organization with a pronounced chain disorganization for the medium- and long-chain derivatives. The mesomorphic properties of ferrocene-containing thermo- tropic liquid crystals have recently been reviewed.' Among the structures reported so far,' 1,3-disubstituted ferrocene- containing liquid crystals' are of particular interest.Indeed, 1,3-substitution led to thermotropic materials which exhibited remarkable liquid-crystalline properties compared with those obtained for the 1,l'-and 1,2-isomeric analogues: the 1,3-disubstituted ferrocene derivatives showed enantiotropic nematic and/or smectic C phases: while their 1,l'-isomeric analogues (series I in ref. 3) gave only monotropic nematic phases (for the short-chain derivatives) and their 1,2-isomeric analogues (structure 18 in ref.1) were found to be non-mesomorphic. The origin of the strong liquid-crystalline character resulting from 1,3-disubstitution can be explained on the basis of structural considerations. First, the two substituents, located on each side of the cyclopentadienyl ring, are disposed in a coplanar arrangement. Such a situation, provided that the rigid rod is sufficiently long, can thwart the unfavourable steric effect of the bulky ferrocene core, which strongly decreases the mesomorphic behaviour (with respect to the ferrocene-free material) when incorporated into a mesogenic structure. The tendency of the ferrocene unit in decreasing the liquid-crystalline properties, was also clearly established in the case of 1,l'-disubstituted ferrocene derivative^.^ Secondly, the X-ray crystal structure determined for one derivative2" revealed a highly anisotropic structure for the 1,3-disubstituted ferrocene derivatives, so allowing favourable intermolecular attractions.More information is required to understand fully the structure-mesomorphic properties relationship for the 1,3-disubstituted ferrocene derivatives, particularly concerning their supramolecular organization in liquid-crystalline states. Therefore, to explore further the capability of such structures for forming liquid-crystalline materials, we describe the prep- aration, mesomorphic properties and X-ray diffraction studies of the new ferrocene derivatives I.These compounds differ from those previously reported2 by the orientation of the external ester functions. Results and Discussion Syntheses Ferrocene derivatives I were prepared by reaction of the ferrocene 1,3-diacid chloride' with the 4-alkoxyphenyl 4-hydro~ybenzoates~(n=5-8,10,12,14,16,18) in dry CH2C12, at reflux, in the presence of Et,N. Purification by column chromatography (Silica gel; CH2C12-AcOEt, 50:l v/v) and crystallization from CH,Cl,-EtOH gave the desired com- pounds in 70% yield. The structures were confirmed by 'H NMR spectroscopy and elemental analysis. Mesomorphic Properties The transition temperatures and enthalpy changes were deter- mined by differential scanning calorimetry (DSC) and are reported in Table 1.The mesophases were identified by a combination of thermal polarized optical microscopy and X-ray diffraction. The phase diagram of compounds I is illustrated in Fig. 1. All ferrocene derivatives I exhibited a strong liquid- crystalline character. The first member of the series, 1 (n=5), showed an enantiotropic nematic phase associated with a broad liquid-crystal range (62 "C). On cooling from the isotropic state, a monotropic smectic A phase formed after the nematic phase. Owing to the high clearing temperature, slight decomposition was detected in the isotropic liquid. The ferrocene derivatives I (n=6) and I (n=7) exhibited two Table 1 Phase-transition temperatures/"C" and enthalpy changes/kJ mol-' of ferrocene derivatives I n C-SA SC-SA C-N SA-N SA-I N-I 186 (178)b,c -248 32.6 2.6 6 191 --219' -239 47.1 3.2 7 190 --228 -233 41.3 1.o 3.4 8 190 ---228 -45.0 7.4 -10 185 ---227 44.9 10.5 12 178 ---223 -43.3 11.6 14 174 ---219 -43.8 12.4 16 171 ---213 -40.4 13.7 18 168 ( 163)b3' --208 -43.2 13.0 C =crystal; N =nematic phase; SA=smectic A phase; Sc =smectic C phase; I =isotropic liquid.Monotropic transition. 'Observed by polarized optical microscopy only. J. MATER. CHEM., 1994, VOL. 4 To strengthen the interpretation given from the observations 270 obtained by polarized optical microscopy, and to gain infor- mation about the molecular organization within the liquid- .-F \ crystalline states, the smectic phases of the ferrocene deriva- 1501 I I I I I , (SC) I 6 8 10 12 74 16 18 20 alkyl chain length Fig.1 Phase diagram of ferrocenes I. 0,Melting point; +, clearing point; A, smectic A-nematic transition; 0,smectic A-smectic C transition; A, nematic-smectic A transition. enantiotropic mesophases, a smectic A phase and a nematic phase. Compounds I (n=8, 10, 12, 14, 16) gave rise to enantiotropic smectic A phases with large anisotropic domains. Finally, the last member of the family, I (n =18), showed two mesophases, a broad enantiotropic smectic A phase and a monotropic smectic C phase. Typical textures were observed by means of polarized optical microscopy. When I (n=5-7) were cooled from the isotropic liquid, the nematic phases appeared either in the schlieren texture or in the homeotropic one.In the latter case, bright flashes were observed when the preparation was touched with a spatula. The nematic to smectic A transition was clearly detected by polarized optical microscopy and in one case, i.e. for I (n=7), also by DSC. When ferrocene derivatives I (n=8, 10, 12, 14, 16, 18) were cooled from the isotropic liquid, focal-conic fan textures and, in several cases, homeotropic zones, both characteristic of the smectic A phases, were observed. For I (n= 18), the smectic A to smectic C transition was identified by the formation of a schlieren texture from the previous homeotropic zones, and by the transformation of the focal-conic fan texture (Plate 1) into the broken focal-conic fan texture (Plate 2).tives I (n=6, 8, 10, 18) were analysed by X-ray diffraction. The nature of the srnectic A phases was thus clearly confirmed. Each of these compounds gave similar data, i.e. X-ray patterns presenting a sharp ring in the low-angle region and a diffuse one in the wide-angle region. The monotropic smectic C phase of I (n =18), which crystallized during experiment owing to its short existence range (SA-Sc, 163 "C; Sc-C, 158 "C),could not be characterized by X-ray diffraction. The layer spacing, d, obtained by X-ray diffraction, the molecular length, L, measured from CPK models, and the corresponding d/Lratio are reported in Table 2. For the fer- rocene derivatives I (n=6) and I (n=8), the d/L ratio ranged between 0.9 and 1.0 and indicated a monolayer arrangement of the molecular units in the smectic A phases.On increasing the alkyl chain length, i.e. for compounds I (n= 10) and I (n=18), the d/L ratio decreased to 0.78 [I (n=18)]. The discrepancy between the layer spacing and the molecular length can be attributed to the pronounced disorganized state of the long alkyl chains which can fold easily owing to the lateral bulkiness of the ferrocene moiety. However, we cannot exclude that the low d/L values may also originate from intensive orientational fluctuations or from pre-existing smectic C correlations in the smectic A phase. These results are in agreement with literature data reported for other metallomesogens.6 Table 2 Layer spacing of ferrocene derivatives I 6 42.1 200 46 0.92 8 50.1 200 51 0.98 10 49.6 200 57 0.87 18 59.9 190 77 0.78 ~ ~~ a From X-ray diffraction.conformation. From CPK models in the fully extended Plate 1 Thermal optical micrograph of the focal-conic fan texture displayed by I(n= 18) in the smectic A phase upon cooling from the isotropic liquid to 204.7 "C J. MATER. CHEM., 1994, VOL. 4 681 Plate 2 Thermal optical micrograph of the broken focal-conic fan texture displayed by I(n= 18) in the smectic C phase upon cooling from the smectic A phase (see Plate 1) to 154.8 "C Fe I (n=5-8,10,12,14,16,18) The strong liquid-crystal character shown by ferrocene derivatives I can be interpreted on the basis of structural features.In fact, in a previous report,% by comparing the thermal properties of two families of ferrocene derivatives substituted in the 1,3-positions, we demonstrated that meso- morphism develops from an l/l' ratio>5-7 (l=length of the rigid rod; I' =distance between the two cyclopentadienyl rings of the ferrocene unit). In the present study, the length I of the rigid segment in I was found to be ca. 27.5 A (in the most extended conformation) from CPK molecvlar models. The depth E' of the ferrocene core being ca. 3.3 A,7 an l/E' ratio of 8.3-8.4 is obtained. Therefore, this value confirms that ferro- cene derivatives I possess the required structural character- istics for exhibiting pronounced mesomorphism. The ferrocene derivatives I and those reported in ref.2 differ in the orientation of the external ester functions. It is interes- ting to point out that, whereas compounds I exhibit smectic A and nematic phases, their isomeric structures gave smectic C and nematic phases.2 These observations, which show the strong influence of the organic substituents on the nature and stability of the mesophases, can be explained in terms of electronic effects, Owing to the C, symmetry of compounds I (and of their isomeric analogues2), local effects can be considered. The organic fragments 1and 2 were used for constructing ferrocene derivatives I and their isomeric analogues: respect-ively. In structure 1,electron delocalization takes place in the interior of the organic fragment. In structure 2, electron delocalization occurs in the opposite direction, from the 0 atom of the alkoxy chain to the ester function.Consequently, (1) electron delocalization is more extended in 2 than in 1, and (2) the 0 atom of the ether group is more polar in 2 than in 1. The electron delocalization presented above which leads to different intermolecular interactions for each organic fragment is, most likely, at the origin of the different mesomorphic behaviour observed between the two isomeric series. Such results, which were also observed for isomeric 1,l'-disubstituted ferrocene derivatives: are in agreement with literature data reported for wholly organic liquid crystak8 Finally, the liquid-crystal ranges reported herein, and those exhibited by the first family of 1,3-disubstituted ferrocene derivatives,2 represent the largest anisotropic domains observed to date in case of ferrocene-containing thermotropic liquid crystals.1 2 Conclusions The synthesis and characterization of the second family of homologous 1,3-disubstituted ferrocene-containing thermo- tropic liquid crystals are described. Ferrocene derivatives I exhibited broad enantiotropic smectic A and/or nematic phases. X-Ray investigations suggested a molecular organk- ation into monolayers with an important chain disorganiz- ation for the medium and long-chain derivatives (n= 10, 18) within the smectic A phases. The present results, and those recently described,' clearly show that 1,3-disubstituted ferro- cene-containing thermotropic liquid crystals, owing to their high thermal stability and pronounced mesomorphic charac- ter, are valuable metallome~ogens.~ Furthermore, the electro- chemical characteristics of the ferrocene unit,7 which can be reversibly oxidized into the ferrocenium species, combined with the mesomorphic properties of the 1,3-disubstituted ferrocene derivatives, make such compounds interesting candi- dates for elaborating liquid-crystalline materials from elec- troactive molecular units.Experimental General Ferrocene-l,3-diacid chloride,' and the 4-alkoxyphenyl 4-hydroxyben~oates~were prepared as in the literature. Column chromatography (CC) used Silicagel 60 (0.063-0.200 mm, Merck) and TLC used Silicagel plates (Merck).Transition temperatures and enthalpies were deter- mined with a differential scanning calorimeter (Mettler DSC 30) connected to a Mettler-TA 3000 system, rate 10 "C min-' under N2. Optical studies were conducted using a Zeiss-Axioscop polarizing microscope equipped with a Linkam-THMS-600 variable temperature stage under N2, A Bruker AMX 400 spectrometer at 400.13 MHz was used for 'H NMR spectra. X-Ray diffraction patterns of powder samples in Lindemann capillaries were recorded photographically at several temperatures using a Guinier focusing camera equipped with a bent quartz monochromator (Cu-Ka, radi- ation from a Philips PW-1009 generator) and an electrical oven. Elemental analyses were conducted by Ciba SA, Marly, Switzerland. Syntheses The general synthetic procedure of bis [4-(4-alkoxyphenoxy-carbony1)phenyll ferrocene-1,3-dicarboxylatesI is exemplified by the preparation of bis [4-( 4-pentyloxyphenoxy- carbony1)phenyll ferrocene-1,3-dicarboxylateI (n=5).A mix- ture of ferrocene-1,3-diacid chloride (0.1g, 0.32 mmol), 4-pentyloxyphenyl 4-hydroxybenzoate (0.194 g, 0.65 mmol), Et,N (66 mg, 0.65 mmol), a catalytic amount of 4-pyrrolidinopyridine and CH,Cl, (10 cm3) was heated at reflux for 3 h. The solution was cooled to room temperature and evaporated. Purification of the resulting residue by CC (Silica gel, CH,Cl,-AcOEt 50:1, v/v) and crystallization from CH2C12-EtOH gave the desired compound in 70% yield. 'H NMR (CDCl,, TMS) dH: 0.94 (6 H, t, 2 x CH3), 1.42 [8 H, m, 2x(CH,),], 1.80 (4H, m, 2xCH2CH,0), 3.97 (4H, t, 2 x CH2CH20), 4.48 (5 H, S, Cp), 5.28 (2 H, d, Cp), 5.80 (1 H, J.MATER. CHEM., 1994, VOL. 4 Table 3 Elemental analytical data of ferrocene derivatives I (calculated values in parentheses) n C(%) H(%) 5 68.76( 68.74) 5.59( 5.53) 6 69.06 (69.29) 5.58( 5.81) 7 69.87( 69.80) 6.14( 6.08) 8 70.27( 70.28) 6.42( 6.34) 10 70.86( 71.16) 6.87( 6.80) 12 7 1.84( 7 1.94) 7.30( 7.21) 14 72.55 (72.65) 7.39( 7.57) 16 73.22( 73.28) 7.78( 7.91) 18 73.87( 73.86) 8.06(8.21) t, Cp), 6.94 (4 H, d, 2 x 2H-arom.), 7.13 (4 H, d, 2 x 2H-arom.), 7.35 (4 H, d, 2 x 2H-arom.), 8.29 (4 H, d, 2 x 2H-arom.). IR (KBr) v,Jcm-': 3132, 2933, 2869, 1733, 1604, 1467, 1415, 1120, 1103, 869, 834, 814.Found: C, 68.76, H, 5.59; calc. for C48H46010Fe (838.74): C, 68.74, H, 5.53%. Ferrocene derivatives I (n=6-8, 10, 12, 14, 16, 18) gave analytical data which were in agreement with their structure (Table 3). One of the authors (R.D.) acknowledges Ciba S.A, Marly, Switzerland, for the elemental analyses, Chemische Betriebe Plutopeba Oel AG, Germany, for a generous gift of acetyl ferrocene used to prepare ferrocene-1,3-dicarboxylicacid, and the Swiss National Science Foundation for financial support. References 1 R. Deschenaux and J. W. Goodby, in Ferrocenes. From Homogeneous Catalysis to Materials Science, ed. T. Hayashi and A. Togni, VCH Verlagsgesellschaft, Weinheim, in the press. 2 (a) R. Deschenaux, I.Kosztics, J-L. Marendaz and H. Stoeckli- Evans, Chimia, 1993, 47, 206; (b) R. Deschenaux and J-L. Marendaz, J. Chem. SOC., Chem. Commun. 1991,909. R. Deschenaux, J-L. Marendaz and J. Santiago, Helv. Chim. Acta, 1993,76, 865. N. J. Thompson, J. W. Goodby and K. J. Toyne, Liq. Cryst., 1993, 13,381. M. Hisatome, 0. Tachikawa, M. Sasho and K. Yamakawa, J. Organomet. Chem., 1981, 217, C17; A. Kashara, T. Izumi, Y.Yoshida and I. Shimizu, Bull. Chem. SOC. Jpn., 1982,55,1901. 6 M. Ghedini, D. Pucci, E. Cesarotti, P. Antogniazza, 0. Francescangeli and R. Bartolino, Chem. Muter., 1993, 5, 883; E. Campillos, M. Marcos, J. L. Serrano, J. Barbera, P. J. Alonso and J. I. Martinez, Chem. Mater., 1993,5, 1518. 7 C. Elschenbroich and A. Salzer, in Organometal~ics,Verlag Chemie, Weinheim, 1989. 8 Y. Sakurai, S. Takenaka, H. Miyake, H. Morita and T. Ikemoto, J. Chem. SOC., Perkin Trans. 2, 1989, 1199; H. Takeda, Y. Sakurai, S. Takenaka, H. Miyake, T. Doi, S. Kusabayashi and T. Takagi, J. Chem. SOC., Faraday Trans., 1990, 86, 3429; R. Centore, M. R. Ciajolo, A. Roviello, A. Sirigu and A. Tuzi, Liq. Cryst., 1991, 9, 873. 9 S. A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861; D. W. Bruce, in Inorganic Materials, ed. D. W. Bruce and D. OHare, Wiley, Chichester, 1992; P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola, Coord. Chem. Rev., 1992,117, 215; A-M. Giroud-Godquin and P. M. Maitlis, Angew. Chem. Int. Ed. Engl., 1991,30,375. Paper 3/07224J; Received 7th December, 1993
ISSN:0959-9428
DOI:10.1039/JM9940400679
出版商:RSC
年代:1994
数据来源: RSC
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