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Microstructure and Defect Chemistry of Yttrium Aluminium Garnet Ceramics

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Microstructure and Defect Chemistry of Yttrium Aluminium Garnet Ceramics INIS-mf—12558 NL89C1183 MICROSTRUCTURE AND DEFECT CHEMISTRY OF YTTRIUM ALUMINIUM GARNET CERAMICS IV I I Hb | Ilia efc • j — log pO, c _ LOTHAR H. SCHUH r \* Cover: The Defect Diagram Of Ca-Doped YAG MICROSTRUCTURE AND DEFECT CHEMISTRY OF YTTRIUM ALUMINIUM GARNET CERAMICS »•#i-*» MICROSTRUCTURE AND DEFECT CHEMISTRY OF YTTRIUM ALUMINIUM GARNET CERAMICS PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de rector magnificus, prof. ir. H. Tels, voor een commissie aangewezen door het college van dekanen in het openbaar te verdedigen op vrijdag 25 augustus 1909 te 16.00 uur. door LOTHAR HKRBSBT SCHUH geboren te Hermülhelm (West-Duitsland) Dlt proefachrlit la goadfakaurd door da proaotoren Prof. dr. R. Hataelaar •n Prof. dr. a. de With CONTENT 1 INTRODUCTION. i 2 THE GARNET STRUCTURE 4 3 LITERATURE REVIEW: OErECT PROPERTIES OF OARNETS 7 3. 1 IRON GARNETS 7 3. 1. l Oxygen diffusion in YIG 8 3. 1. 2. Cation diffusion In YIG 10 3. 1. 3 Direct determination of oxygen vacancies in YIG 12 3. 1. 4 Electrical conductivity and thermo-electric power in YIG 13 3. 1. 5 Other iron garnets 15 3. 2 YTTRIUM ALUMINIUM AND OTHER GARNETS 15 3. 2. 1 Oxygen diffusion in YAG 16 3. 2. 2 Electrical conductivity in YAG and other non iron garnets 17 3. 3 SITE EXCHANGE EFFECTS IN GARNETS 19 4 LITERATURE REVIEW: COLOUR CENTRES AND PARAMAG- NETIC DErECTS IN OARNETS 23 4. 1 COLOUR CENTRES 23 4. 2 PARAMAGNETIC DEFECTS 26 5 SAMPLE PREPARATION AND EXPERIMENTAL SET UP. 32 5. 1 SAMPLE PREPARATION. 32 5. 2 SINTERING OF THE POWDERS 32 5. 2. 1 Evaporation effects during sintering 33 5. 3 SOLUBILITY OF Ca, Hg, Zr AND Hf IN YAG 36 5. 4 ELECTRICAL MEASUREMENTS 37 5. 4. 1 Electrodes and electrode effects 40 6 ANALYTICAL TECHNIQUES AND RESULTS 47 6. 1 ELEMENT ANALYSIS 47 6. 2 AUGER ANALYSES 47 7 AL-RICH INCLUSIONS 50 7. 1 CHEMICAL COMPOSITION OF THE INCLUSIONS 51 7. 2 THE SHAPE OF THE Al-RICH INCLUSIONS 52 7. 3 THERMAL STABILITY OF THE INCLUSIONS 54 8 6RAIN BOUNDARIES IN TAB INVESTIOATED BY TEM. 56 8. 1 EXPERIMENTAL 58 6. 2 RESULTS AND DISCUSSION 59 6. 3 TEM-STUDIES DESCRIBED IN LITERATURE 62 9 MICROSTRUCTURE AND MICROSTRUCTURAL CIMNBES INVEST I- SATED BX AC-DISPERSIVE MEASUREMENTS 63 9. 1 INTRODUCTION. 63 9. 2 AC-DISPERSIVE DETECTION OF 6RAIH BOUNDARY PHASES IN YAG-CERAMICS 66 I f 9. 2. 1 Experiments and discussion 66 9.3 NON-LINEAR LEAST SQUARES FIT (NLLSF) OF IMPEDANCE DATA 70 9. 4 TEMPERATURE DEPENDENCE OF GRAIN BOUNDARY AND BULK CONDUCTIVITY 74 9. 4. l Experiments and discussion 74 9. 5 A 240 HOURS ANNEAL EXPERIMENT 76 9. 5. 1 Experiments and discussion 77 9. A PROPERTIES OF YAG CERAMIC QUENCHED FROM 2020 K TO ROOM TEMPERATURE 81 9. 6. 1 Experiments and discussion 82 10 DCrCCT CHEMISTRr OT CA- AND MS-DOPED XAB 87 10. 1 SAMPLE CHARACTERISATION. 87 10. 2 DISPERSED PARTICLES IN A CONDUCTING MATRIX: WAGNERS MODEL 88 10. 3 RESULTS AND DISCUSSION 90 10. 4 THE TEMPERATURE DEPENDENCE OF CONDUCTIVITY 100 10. 5 CONCLUSION 102 It DEFECT CHEMISTRr ©T ZR-DOPED XAB 103 11. 1 SAMPLE CHARACTERISATION 104 11. 2 RESULTS AND DISCUSSION 105 11. 2. 1 The defect model for Zr-doped YAG 106 11. 3 THE TEMPERATURE DEPENDENCE OF THE CONDUCTIVITY 109 11. 5 CONCLUSION. 110 12 UNDOPCD POLrCRySTAtL INC TAB 112 12. 1 SAMPLE CHARACTERISATION 112 12. 2 RESULTS AND DISCUSSION 112 12. 3 CONCLUSION 115 13 VNDOPED SINBLE CRYSTALLINE TAB 115 13. 1 SAMPLE CHARACTER I SAT I ON 115 13. 2 EXPERIMENT AND DISCUSSION 116 1 3. 3 CONCLUSION. 118 14 INTERACTION ©T TAB WITH HTDROBEN CONTAININB ATMOSPHERES 119 14. 1 INTRODUCTION. 119 14. 2 INFRARED BANDS IN ANNEALED SINGLE CRYSTALLINE YAG 120 14. 3 ELECTRICAL TRANSPORT PROPERTIES OF YAG IN A Hs/HpO AMBIENT 122 14.3. 1 The activation energies for a in YAG: Zr in H2/H20 123 14. 3. 2 The activation energies for o in undoped YAG in H2/H20 124 14.3.4 The complex impedance behaviour of polycrystal 1 lne YAG in a H2/H2O-atmosphere 126 14. 4 CONCLUSION. 127 15 SINTER ADDITIVES MMD MICROSTRUCTURE 129 15. 1 EXPERIMENTS 129 15. 2 RESULTS AND DISCUSSION 130 15. 3 EXAMPLE OF EXAGGERATED GRAIN GROWTH 133 v tti: tt > ^ 15. 4 CONCLUSION 135 16 COMPUTER SIMULATION Of IONIC DEFECTS 136 16. 1 THEORY OF DEFECT CALCULATIONS-A SKETCH 136 16. 2 THE PERFECT LATTICE PROPERTIES OF YAG 138 16. 3 THE BASIC POINT DEFECT FORMATION ENERGIES 140 16. 4 FOREIGN CATIONS IN YIG AND YAG 141 16. 5 OXIDATION/REDUCTION PROCESSES IN YAG AND YIG 142 16. 6 THE DISSOLUTION OF CaO IN YAG 146 16. 6. 1 The energy for substituting Y by Ca 146 16. 6. 2 The solution enthalpy of CaO In YAG 147 16. 6. 3 Clustering effects 149 16. 7 THE DISSOLUTION OF MgO IN YAG 149 1 6. 0 SADDLE POINT ENERGIES 160 16. 8. 1 Oxygen juaps 150 16. 8. 2 The spatial dependence of the saddle point energies 153 16. 8. 3 AlumlnluB Jumps 155 16. 9 CONCLUSION 155 APPENDIX 1 167 APPENDIX 2 165 SUMHART 166 SAMENVATTINB 168 CURRICULUM VITAE 169 STELLIHGEH 1. The opinion that sintering of solid particles is a vary alow process at room temperature hardly describes reality. S.R.Rao "Surface Phenomena", Hutchinson Educational Ltd., (1972), p. 70 2. The autors conclude that high meat western diet enhances the excretion of the trace element Hn; they did not pay attention to the fact that several components of this diet contain re- latively high amounts of this trace element. Furthermore, tes- ting only 14 men and women does not lead to reliable results. J. H. Johnson, dies, H. M. Fox, Hutr. Rep. Intern, ,3ft, (1966), 1299 3. "YAG-laser: abbreviation for yttrlum-argon-laser" - this statement is not true. Pschyrembel Kllnlsches wbrterbuch, p. 1827, 255. Auflage 1985, W. de Qruyter, Berlin 4. The authors give the temperature dependence of the di- electric from temperature for 92X pure alumina, con- cluding that this is the loss of alumina Itself. They do not take into consideration that liquid phases are presum- ably responsible for loss in highly Impure materials. H. FuKushlma, T. Tamanake, H. Hatsul, Hat. Res. Soc. Symp. Proc. , 121, (1966), 267 5. The extracts of Caplscum Annuum (chile pods), which was proved to serve as a D^-sensltlve coating for a piezo-crystal de- tector is in no way characterized. The speculation that vita- mine c plays an important role is is doubtful. L. H. Webber, a a. Oul 1 baul t, Anal. Cham. , 4ft, (1976). 2244 6. Jeh and Sacks report that they have sintered fine grained alumina powders to 99.5Z density at 1160°C with average grain size of 0.25 pm after 2h sintering time. Hlcrostructural analysis was done on samples which were thermally etched at 116O°C for 4 h. So they investigated samples which were sintered In fact 6 h. T. S. Yeh, H. D. Sacks, J. Am. Ceram. Soc. , H, (1966), 644 7. Die Autonomle, die sle (die Kunst) erlangte, nachitem. sle lhre kultlsche Funktlon und dessen Hachbllder abschilttelte, zehrt von der Idee der Humanltat - Theodor V. Adorno, "Asthe- tlsche Theorle", Suhrkamp Verlag, 1977. In this stage In the development of arts In Hunan society It Is commercialisation and not humanity which acts as a "fertilizer". 8. Sintering behaviour of an alumina powder with a maximum particle diameter of 0. 2 pm is compared with the unclassi- fied powder. Ho particle size distribution of the unclassi- fied powder Is given. T. R. Gattuso, H. E. Bowen, Adv. Cer. , 1£, (1987), 644 9. The electrical conductivity of AlB containing various oxide additives was investigated by dc-methods. Ho frequency dis- persion is given. Due to the fact that AlH-gralns are covered by a highly insulating alumlna-fllm, these results are doubt- ful. H. Zufelquar, A. Kumar, J. Hater. Scl. ,££, (1967), 4056 10. It is not plausible that the misfit strain of a Ca2+-lon on a Al3*-position in AI2O3 Is about 1.5 eV/atom as stated by Cook and Schrott. It must be much higher because the defect Ca^t/ has a charge. R. F. Cook. A. Q. Schrott, J. Am. Ceram. Soc. H, (1966), SO 11. C00K and Schrott considered the segregation of Ca to grain boundaries In alumina; they conclude that the misfit strain Is the driving force for this process. The authors should better consider the solution enthalpy of CaO In alumina as well as the difference In energy for CaA]'(bulk) and CaAJ (grain boundary) R. P. Cook, A. fl. Schrott, J. Am. Ceram. Soc. , 2i, (1966). 50 12. Rotman and Tuller do not consider the possibility that at low oxygen pressure Zr** is reduced. S. R. Rotman, H« L. Tul ler, Hat. Res. Soc. Symp. Proc. £0_, (1966) 413 13. The diffusion In KgSiO3 Is considered at a 3750 K (I) and 37 QPa; a perfect lattice simulation may not lead to accurate results. B. Kapusta, H. (Millope, Phil. Hag. A 3ft, (1966) 6O9 14. The fact that Ahmed et al. found slightly different trans- ition temperatures of 90 and 93 I for conventionally and microwave sintered 1-2-3 superconductors is far from being significant. 1. Ahmed, <3. T. Chandler, D,B. Clark, Hat. Res. Soc. Symp. Proc. 124. (1986), 239. INTRODUCTION Tills thesis is centered around the synthetic garnets, a class of materials with the same crystallographic structure as the natu- rally occurring garnet minerals.
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