A new method on the study of phase transition "Phase Transition seeing by Milli-Kelvin Stabilized cell" Development and Application

这一年来，在BaTiO_3的三个相变的物理性质研究和结构研究方面都取得了很好的成果。阶段-室温低温阶段最低温度阶段阶段）。明确了每一相变的相变机制的本质。本研究中所用的单晶是采用顶部籽晶溶液法生长的，晶体没有完成极化。通过介电常数、位移电流、电阻率测量和共振超声光谱同时测量吸热或放热，明确了每种相变具有不同的转变机制。特别是共振超声谱的结果表明，室温相和低温相的共振谱相对于高温相和最低温度相的共振谱更为复杂。这一结果表明，与高温相和最低温度相相比，室温相和低温相的晶体结构都比较复杂。另一方面，本研究的组织独立地研究晶体的物理性质和通过X射线衍射进行的结构研究。结构研究结果表明，晶体结构发生如下相变：立方晶系-四斜晶系和单斜晶系1的混合结构-正交晶系1和单斜晶系2的混合结构-正交晶系2。这一结果对解释所获得的物理性质具有重要意义，并且与共振超声光谱研究的预期结果吻合良好。

The good fruit of this year was obtained from the results for both researches of the physical properties and structural studies on three phase transitions of BaTiO3 (high temp. phase-Room temp. phase-Low temp. phase-Most low temp. phase). They made clear the nature of the phase transition mechanism of each phase transition. Single crystals used in this study were grown by top-seeded solution growth method and the crystals were not accomplished poling. It was cleared that each phase transition has different transition mechanism by the measurements of dielectric constant, displacement current, dilatometric measurements, and resonant ultrasonic spectroscopy simultaneous with endothermic or exothermic heat measurements. The result of the resonant ultrasonic spectroscopy, especially, showed that resonant spectra for both the room temperature and the low temperature phases are rather complex compare with the both the high temperature and the most low temperature phases. This result suggested that the crystal structures of the both the room temperature and the low temperature phases are complex compare with those of the high temperature and the most low temperature phases. On the other hand, the organization of this research studies on the physical property of the crystal and on the structural study by X-ray diffraction, independently. The results on the structural study showed that the crystal structure changes by the phase transitions as follow; cubic system-hybrid structure of tetragonal and monoclinic 1 systems-hybrid structure of orthorhombic 1 and monocliic 2 systems-orthorhombic 2. The result is important to explain the obtained physical properties and well agrees with the results expected from the resonant ultrasonic spectroscopy study.