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

今年的好成果来自于对BaTiO3的三个相变（高温相-室温相-低温相-极低温相）的物理性质和结构研究的结果。他们明确了每个相变的相变机理的性质。本研究使用的单晶采用顶种溶液生长法生长，晶体未完成极化。通过对介电常数、位移电流、膨胀测量和共振超声光谱与吸热或放热测量的同时测量，明确了每个相变具有不同的转变机理。谐振超声光谱分析结果表明，与高温相和最低温相相比，室温相和低温相的谐振光谱更为复杂。结果表明，与高温相和最低温相相比，室温相和低温相的晶体结构更为复杂。另一方面，本研究组织对晶体物理性质的研究和对x射线衍射结构的研究，独立进行。结构研究结果表明，晶体结构的变化是由相变引起的：四边形和单斜晶系的三次系统-杂化结构-正交1和单斜晶系的杂化结构-正交2。该结果对解释所得到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很好地吻合。

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.