本論文採用還原燒結與受體添加，研究非計量式組成(TiO2過賸)之鈦酸鋇的微結構發展。以X-ray繞射分析結晶相。微結構之分析則採用掃描式電子顯微鏡(SEM)與穿透式電子顯微鏡(TEM)。
低氧氛壓進行還原處理是為了使氧氣缺乏。依據缺陷化學的理論，受體添加也能在無壓燒結下達到與還原處理相同的目的。我們將觀察與分析燒結後的試片，驗證氧空缺的形成使介穩高溫六方相鈦酸鋇保留至室溫。
在添加鎂離子的實驗中，研究在鋇離子與鈦離子兩者中，鎂離子優先替代鈦離子的可能性，是否如同理論上優先選擇相似離子半徑一般。根據穿透式電子顯微鏡(TEM)的分析，找到鎂離子也替代鋇離子的證據。
在氫氣還原處理下，鈦酸鋇轉變為深色導體(high dark conductivity)。鈦離子由四價轉為三價是變深色的原由。其缺陷化學方程式可寫為 。試片上巨觀的體積變化，證明了在控制氧氛壓下，產生了多種微結構。
藉由穿透式電子顯微鏡(TEM)的繞射分析(reciprocal lattices)，推導出一轉置矩陣(transformation matrix)來描述雙晶(twinning)的關係。在反晶格(reciprocal lattices)的研究上，分析出在雙晶(twinning)的晶界上(BaO3層)形成氧空缺。並利用X-ray的鑑定與表面能(surface energy) 的分析，確定了在低氧氛壓下雙晶(twinning)越來越多的趨勢。根據雙晶晶界(twin boundary)處形成氧空缺的論點，越低的氧氛壓造成越多的雙晶(lamellae twins)。經由模擬，高溫六方相鈦酸鋇的原子結構確實可以以常溫正方相鈦酸鋇以每三層產生一個雙晶(twinning)的方式表達。這證明了氧空缺的形成使介穩高溫六方相鈦酸鋇保留至室溫。

Non-stoichiometric barium titanate (BaTiO3) powder of TiO2-excess compositions has been investigated using both reducing sintering and acceptor-doping. Crystalline phases were analysed by XRD. Attention has been paid to the analysis of the corresponding sintered microstructure by adopting scanning and transmission electron microcopy.
Reducing sintering was in the low oxygen partial pressure, so as to dominate the oxygen-deficient. According to the defect chemistry, the purpose of acceptor-doping was the same as reducing sintering. We look out for phenomena which may be indicative that oxygen vacancies generated by acceptor-doping and reducing sintering have resulted in the metastable retention of high temperature hexagonal-BaTiO3 to an ambient temperature.
In the Mg-doped study investigated the possibility that Mg2+ substitutes on Ti4+ site rather than the Ba2+ site, as expected from the radii. According to the unknown phase was indexed a supercell of MgTiO3, that showed evidence of Mg2+ dissolves in BaTiO3 and occupies the Ba2+ site.
To reduce in a hydrogen atmosphere was a high dark conductivity. The Ti3+ content was determined via colorimetry. Because of the defect chemistry led to oxygen-deficient h-BaTiO3, i.e.BaTi1-xTixO3-x/2. The observed volume expansion behavior under Ar-H2 atmosphere demonstrates the possibility of having various microstructures via control of oxygen partial pressure.
The transformation matrix described the relation between the two reciprocal lattices of the twinning. Investigation of reciprocal lattices was shown that ordering oxygen deficient on the BaO3 layer in the twin boundary. There was evidence of XRD patterns and surface energy that explained more and more twins in the microstructure via control of the low oxygen partial pressure. According to this theory, lamellae twins were generated by oxygen-deficient. The hexagonal phase might be also expressed as the cubic BaTiO3 containing twin boundary at BaO3 planes every three layers. That demonstrates the possibility of hexagonal phase retention in BaTiO3 was oxygen vacancies.

Abstract ………………………………………………………………………….. I
Contents ………………………………………………………………………... III
List of Tables …….………………………………………………………….... VII
List of Figures …………….……………………………………………….... VIII

Chapter 1 Introduction ………..…………………………………………... 1

Chapter 2 Survey of relevant literature .……………………………… 2
2.1 Perovskite - Basic Information ……...………………….............. 2
2.2 Crystal structure of BaTiO3 .............……………………...…….... 5
2.2.1 Structure of tetragonal-BaTiO3 ………………….......... 6
2.2.2 Structure of hexagonal-BaTiO3 …………………..…… 9
2.3 Equilibrium phase diagrams of the BaO-TiO2 system ………….. 12
2.4 Abnormal grain growth in BaTiO3 ..…………………….……… 18
2.5 Hexagonal related perovskite (polytypes) ……………………… 18
2.6 Defect reaction for MgO-doping ……………………………….. 21
2.6.1 Compensation effect in semiconducting Barium Titanate (Mg-doped) …………………………………………….
22
2.7 Properties of BaTiO3 ……………………………………………. 23
2.8 Diffraction contrast ……………………………………………... 24
2.8.1

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