STUDY ON THE DIELECTRIC PROPERTY AND PHASE TRANSITION OF PEROVSKITE STRUCTURE TYPE RELAXOR MATERIALS

本研究旨在探讨铅基钙钛矿材料的电学性能与晶体结构的关系，明确其扩散相变的机理。首先从晶体结构和电子结构的角度研究了锰对锆钛酸铅（PZT）机电性能的影响。然后，证实了Mn的加入使压电陶瓷具有高耦合系数和低机械损耗的压电材料。阐明了Mn掺杂PZT的高耦合系数源于Mn的加入导致轴比c/a的降低，而低机械损耗是由于Mn3+和/或Mn2+为电荷补偿而引入的氧缺陷的存在。其次，研究了铅镁铌氧化物（PMN）扩散相变的机理。以下事实得到证实。1)PMN在-40℃下呈现铁电性，铁电性程度随温度的降低而增大。2) PMN的晶体结构在-100℃时保持立方结构。3)PMN在0℃附近表现出较大的介电色散，在0℃附近存在离子跳变。根据这些结果，我们假设了PMN扩散相变的以下模型。PMN具有尺寸小于x射线相干长度的铁电微畴，其区域随着温度的降低而变大。它在室温附近有热波动，这种波动与离子跳跃有关，它们的弛豫频率随温度的降低而降低。在Tc附近，PMN在1000kHz下表现出较大的介电色散，因为在此附近发现了弛豫频率。结果表明，PMN的弥漫性相变是铁电微畴区域增加，微畴随温度降低而冻结波动的现象。

This study was carried out in order to investigate the relationship between electrical properties and crystal structures of lead based perovskite materials and make the mechanism of diffused phase transition of them clear.At first, effect of Mn addition to lead zirconate titanate (PZT) on electromechanical properties was studied from viewpoints of crystal and electronic structures. Then, it was confirmed that Mn addition made PZT a piezoelectrics with both high coupling factor and low mechanical loss. It was clarified that the high coupling factor of Mn-doped PZT was originated from the decrease in the axis ratio c/a caused by Mn addition and that the low mechanical loss was caused by the existence of oxygen defects introduced with Mn3+ and/or Mn2+ for charge compensation.Secondary, we studied the mechanism of the diffused phase transition of lead magnesium niobium oxide (PMN). The following facts were confirmed. 1)PMN shows ferroelectricity under -40C and the degree of the ferroelectricity increases with the decrease in temperature. 2)The crystal structure of PMN keeps cubic one down to -100C. 3)PMN shows large dielectric dispersion around 0C and there are ion hoppings near 0C. From these results, we supposed the following model related to the diffuse phase transition of PMN. PMN has ferroelectric micro domain which size is smaller than coherent length of X-ray and the region of it become large as temperature decreasing. It thermally fluctuates near the room temperature and the fluctuation relates to the ion hoppings and the relaxation frequency of them decreases with the decrease in temperature. Around Tc, PMN shows a large dielectric dispersion under 1000kHz because the relaxation frequency is found near there. As a result, it was clarified that the diffuse phase transition of PMN was a phenomenon originated from the increase in the region of the ferroelectric micro domain and the freezing of the micro domain fluctuation with the decrease in temperature.