Structural study on the phase transition and physical properties of alkaline niobate-type ferroelectric compounds

本文从结构的观点研究了碱金属钛酸盐铁电单晶的相变及其物理性质的变化。高温下的高精度单晶X射线衍射研究揭示了铌原子配位数和自发极化的系统变化。从Gram-Charlier展开级数确定顺电立方相的非简谐原子位移参数，以获得联合概率密度函数和单粒子势。这些分析揭示了强的一维相关的氧原子沿着的-O-Nb-O-Nb-链的存在下，表明可能的成核和生长的小的四方铁电畴的顺电矩阵的立方相刚好在相变点以上。对相关化合物进行了结构研究。

Phase transitions and associated changes in physical properties of the alkaline niobate ferroelectric single-crystals, have been investigated from a structural point of view. A high-precision single-crystal X-ray diffraction study at elevated temperatures revealed a systematic change in the coordination number of niobium atoms and the spontaneous polarization. The anharmonic atomic displacement parameters of the paraelectric cubic phase were determined from the Gram-Charlier expansion series, in order to obtain the joint-probability density function and the one-particle potential. These analyses revealed a presence of strong one-dimensional correlation of O atoms along the -O-Nb-O-Nb- chain, suggesting possible nucleation and growth of small tetragonal ferroelectric domains in the paraelectric matrix of the cubic phase just above the phase transition point. Structural studies were also carried out on the related compounds.