本論文以無壓力燒結鈦酸鋇陶瓷技術，長時間燒結促進晶粒尺寸長大，且利用穿透式電子顯微鏡觀察分析排差圈。結合“影像對比分析g•b = 0準則”及“影像內-外側法”，求得差排圈的卜格向量為[100]。採用“影像內-外側對比法”分析(g•b)sg值，得知差排圈乃由空缺所造成。以差排圈的高解析穿透式電子顯微鏡影像進一步確定差排圈卜格向量為1/2[100]，且為空缺造成，負向部份差排橫臥於{200}。在鈦酸鋇晶粒中，局部TiO2-空缺藉由空缺差排圈的形成來調節適應。推測差排圈的形成原因，乃是鈦原子及氧原子空缺在非計量無壓力燒結過程中，局部聚集所導致。

Dislocation loops in pressureless-sintered undoped BaTiO3 ceramics have been analysed via transmission electron microscopy (TEM). The Burgers vector b = [100] of the loops was initially determined by the contrast analysis of the g•b = 0 criteria combining with the inside-outside contrast method by which the sense of the Burgers vector was concluded. The vacancy nature were determined by adopting the inside-outside contrast analysis using the criteria of (g•b)sg being positive or negative when the loops were imaged under kinematical diffraction conditions of sg ≠ 0. High-resolution imaging of such loops has enabled us to confirm its vacancy nature, consistent with the contrast analysis. Further, the loops’ Burgers vector was determined to be b = 1/2[100] and the loops were therefore negative partial dislocation loops lying in {200} where part of the TiO2-deficiency existed locally in the grains of sintered BaTiO3 ceramics was accommodated by the presence of vacancy loops. It is suggested that the extrinsic defects of both titanium and oxygen vacancies ( and ,) generated by the non-stoichiometry which gave clustered during sintering in air are responsible for the formation of the dislocation loops.

Abstract…………………………………………………………………………….i
Content……………………………………………………………………………..iii
List of Figures……………………………………………………………………...v
List of Tables……………………………………………………………………….x
Chapter 1 Introduction…………………………………………………………..1
Chapter 2 Literature Review
2.1 The structure of perovskites……………………………………….. 2
2.2 Crystal structure of BaTiO3………………………………………... 2
2.3 Structure of tetragonal-BaTiO3………………………………...... 5
2.4 Equilibrium phase diagram of the BaO-TiO2 system…………….. 9
2.5 Abnormal grain growth in BaTiO3………………………………..... 17
2.6 Ferroelectric domains……………………………………………..... 17
2.6.1 Types of ferroelectirc domains…………………………………….. 17
2.7 Defect chemistry of BaTiO3……………………………………….... 21
2.7.1 Intrinsic defects………………………………………………....... 21
2.7.2 Extrinsic defects……………………………………………………... 22
2.8 Dislocation in tetragonal-BaTiO3………………………………….. 22
2.9 Dislocation loops in tetragonal-BaTiO3…………………………… 25
Chapter 3 Experimental Procedures
3.1 Initial powders……………………………………………………..... 27
3.2 Preparation of samples…………………………………………….... 27
3.3 Characterisation of sintered samples……………………….……. 29
3.3.1 X-ray diffractometry…………………………………………........ 29
3.3.2 Scanning electron microscopy…………………………………….... 29
3.3.3 Transmission electron microscopy………………………………….. 30
3.3.4.1 Thin foil preparation…………………………………………....... 31
3.3.4.2 Bright-field and dark-field imaging techniques……………….. 34
3.3.4.3 Weak-beam dark-field imaging………………………………........ 34
Chapter 4 Results
4.1 XRD results………………………………………………………....... 37
4.2 Features of OM and SEM…………………………………….......... 40
4.3 Features of TEM…………………………………………………....... 47
4.3.1 Determining the direction of Burgers vector for dislocation loop… 53
4.3.2 Sense of Burgers vector and loop nature…………………………. 54
4.3.2.1 The (g•b)sg-rule…………………………………………………….... 61
4.3.2.2 Determination of the loop nature………………………………….. 61
4.3.3 High-resolution imaging…………………………………………..... 62
Chapter 5 Discussion
5.1 Burgers vector and atomic model of dislocations……………... 73
5.2 How would have the dislocation loops been formed?……....... 87
Appendices
A-1 JCPDS cards for compounds related to this study………………. 91
A-2 Calibration of 3010AEM…………………………………………...... 96
A-3 Kikuchi SADPs for tetragonal-BaTiO3…………………….……….. 97
A-4 The stereographic projection for tetragonal-BaTiO3………….. 98
A-5 Analysis zones of tetragonal-BaTiO3……………………….…….. 99
References…………………………………………………………………..... ... 102

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