THEORETICAL APPROACH ON PHASE TRANSITION AND PHYSICAL PROPERTIES DUE TO QUANTUM EFFECT IN PEROVSKITE-OXIDES

在钙钛矿型氧化物中，几个重要的物理性质被称为反常电导及其有用的应用(例如，用于高电容电容器和电致伸缩执行器的不含铅的铁电材料，具有顺电(PE)-铁电(FE)转变的量子顺电材料，以及与钙钛矿相关的氧化物的高温超导电性。)在这个研究项目中，我们关注了氧八面体网络，并研究了具有本征量子效应的结构的特征声子性质。从微观角度运用解析理论方法，取得了丰硕的成果。具体内容分为四个方面。通过对氢在临时形成的O-H-O键上和键之间扩散的量子力学计算，提出了质子电导率作为清洁燃料基本机理的CELSA质子传导模型，并预测了受主掺杂PE-…中的最佳路径。更多的钙钛矿型氧化物。通过改变O-八面体的网络，明确了量子氢运动和非量子锂扩散的区别。通过推广横向光学声子的软模理论，成功地解释了外加压力和氧同位素160-180取代的量子PE-FE相变。还从微观角度研究了相变点的量子临界指数。弛豫铁电性与准同型相界在有序-无序型相变的微观理论中，提出了弛豫行为的定义，以区别于玻璃性质。讨论了X射线漫反射和核磁共振NQR谱，给出了钙钛矿型氧化物发生位移型转变后出现驰豫的条件。高温超导性我们成功地阐明了纵向光学声子在高温超导体中的作用。对于某些类型的钙钛矿型氧化物，用一个扩展的实空间表示的类BCS方程成功地解释了TC中的160-180同位素效应。提出了准粒子介导的库珀对的概念。较少

In Perovskite-type oxides, several important physical properties are known as anomalous conductivities and the useful applications (for example, Pb-excluded ferroelectrics applied to high capacitance condensers and electrostrictive actuators, quantum paraelectrics with paraelectric (PE)-ferroelectric (FE) transition, and furthermore, high-temperature superconductivity in perovskite-related oxides.) In this research project, we have paid attention to the oxygen octahedron network, and investigated the characteristic phonon properties to the structure with intrinsic quantum effect. The fruitful results were obtained from analytic theoretical approach in the microscopic viewpoint.The contents are divided under the following four heads.1. Proton conductivity as the basic mechanism of clean fuel cellsA model of proton conduction was proposed basing on quantum mechanical calculation for H-diffusion on and between temporally made O-H-0 bond, and optimum path was predicted in acceptor-doped pe … More rovskite-oxides. The difference between quantum H-motion and no-quantum Li-diffusion was made clear by changing the network of O-octahedron.2. Quantum ParaelectricityBy extending soft mode theory for transverse optical phonon, quantum PE-FE transition was explained successfully for applied pressure and oxygen isotope 160-180 substitution in a unified picture. The quantum critical exponent at the transition point was also investigated in a microscopic approach.3. Relaxor ferroelectricity with morphotropic phase boundaryThe definition of relaxor behaviors was proposed to distinguish from glass properties in the microscopic theory for order-disorder type transition. X-ray diffuse scattering and NMR-NQR spectra were discussed, and the conditions for relaxor appearance were presented in perovskite-oxides following displacive-type transition.4. High-temperature superconductivityWe succeeded to make clear the role of the longitudinal optical phonon in superconductors with high transition temperature Tc. For some types of perovskite-related oxides, 160-180 Isotope effect in Tc was explained successfully in an extended BCS-like equation with real-space representation. The idea of quasi-particle mediated Cooper-pair was also presented. Less