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

在钙钛矿型氧化物中，一些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伸缩致动器的不含pb的铁电体，具有准电（PE)-铁电（FE）过渡的量子准电体，以及钙钛矿相关氧化物中的高温超导性）。本课题以氧八面体网络为研究对象，研究了具有本征量子效应的氧八面体结构的特征声子性质。从微观的观点出发，用解析理论的方法得到了富有成效的结果。内容可分为以下四大类：1。质子电导率是清洁燃料电池的基本机理，基于量子力学计算，提出了氢在临时形成的O-H-0键上和键间扩散的质子电导率模型，并预测了在受体掺杂下质子电导率的最佳路径。通过改变o-八面体的网络，明确了量子h运动与非量子li扩散的区别。通过推广横向光学声子的软模理论，成功地解释了在施加压力和氧同位素160-180取代下的量子PE-FE跃迁。用微观方法研究了过渡点处的量子临界指数。为区别于有序-无序型相变微观理论中的玻璃性质，提出了弛豫行为的定义。讨论了钙钛矿氧化物的x射线漫射和核磁共振- nqr谱，并给出了钙钛矿氧化物在置换型转变后出现弛豫的条件。高温超导性我们成功地阐明了纵向光学声子在高转变温度Tc超导体中的作用。对于某些类型的钙钛矿相关氧化物，在实空间表示的扩展类bcs方程中成功地解释了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。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