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

从结构的角度研究了碱性铌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。利用Gram-Charlier展开级数确定了拟电立方相的非调和原子位移参数，得到了联合概率密度函数和单粒子势。这些分析表明，O原子沿-O- nb -O- nb -链存在很强的一维相关性，表明在相变点上方的立方相准电矩阵中可能存在小的四方铁电畴的成核和生长。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.