Title page for etd-0626104-165948


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URN etd-0626104-165948
Author Che-chi Lee
Author's Email Address kadison_@msn.com
Statistics This thesis had been viewed 5335 times. Download 1112 times.
Department Materials Science and Engineering
Year 2003
Semester 2
Degree Master
Type of Document
Language English
Title An analysis hexagonal phase retention in BaTiO3
Date of Defense 2004-06-26
Page Count 157
Keyword
  • MgO-doped
  • reduced
  • phase-transition
  • oxygen-vacancy
  • domain
  • twins
  • BaTiO3
  • Abstract 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.
    Advisory Committee
  • Bing-hwait Hwang, - chair
  • Cing-li Hu - co-chair
  • Chih-hsiung Hsu - co-chair
  • Hong-yang Lu - advisor
  • Files
  • etd-0626104-165948.pdf
  • indicate access worldwide
    Date of Submission 2004-06-26

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