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异常导电性和有用的应用（例如，应用于高电容电容器和电致伸缩致动器的不含Pb的铁电体，具有顺电（PE）-铁电（FE）转变的量子顺电体，以及钙钛矿相关氧化物中的高温超导性。在本研究计划中，我们关注了氧八面体网络，并研究了具有内禀量子效应的结构的特征声子性质。本文从微观的角度，运用分析理论方法，取得了丰硕的成果，主要内容分为以下四个方面：1.质子传导是洁净燃料电池的基本机理，本文基于量子力学计算，提出了质子传导的模型，并预测了受主掺杂的质子在O-H-O键上和键间的最佳扩散路径。 ...更多信息 钙钛矿氧化物通过改变O-八面体的网络结构，明确了量子H运动与非量子Li扩散的区别。量子顺电性通过推广横光学声子的软模理论，在统一的图象中成功地解释了外加压力和氧同位素160-180替代的量子PE-FE跃迁。从微观角度研究了相变点的量子临界指数.准同型相界弛豫铁电性提出弛豫行为的定义，以区别于有序-无序型相变微观理论中的玻璃性质。讨论了X射线漫散射谱和NMR-NQR谱，给出了钙钛矿氧化物发生位移型相变后弛豫出现的条件.高温超导我们成功地阐明了高转变温度超导体中纵光学声子的作用。对于某些类型的钙钛矿型氧化物，160-180同位素效应的Tc成功地解释了一个扩展的BCS类方程与实空间表示。提出了准粒子介导的库珀对的概念。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