在铌镁酸铅-锡酸铅-钛酸铅（PMN-PSn-PT）铁电单晶中观察到异常的铁电压电响应行为：（1）完全偏离一侧的电滞回线；（2）单晶体在未极化的情况下具有高的压电系数d33 （1350 pC/N）；（3）在高于居里温度的温度热处理后，压电系数没有下降，没有出现退极化。我们称这种异常铁电压电响应行为为压电记忆效应。针对压电记忆效应现象，我们提出了点缺陷诱导压电记忆效应的理论模型：在晶体生长过程中产生的点缺陷导致了缺陷极化的产生，长程有序的缺陷极化提供了自发极化择优取向的驱动力和温度稳定性的回复力，从而导致自极化态能稳定存在。本项目就是以PMN-PSn-PT铁电单晶压电记忆效应的物理机制为研究对象，研究其中涉及到的几个关键基础问题，包括单晶的晶格结构、电畴组态、缺陷分布和作用。通过阐明结构、电畴、点缺陷与铁电压电响应行为的关系，来完善压电记忆效应的物理机制。利用这种机制获得开发新材料的方法。

Unusual ferroelectric and piezoelectric response behavior was discovered in Pb(Mg1/3Nb2/3)O3-PbSnO3-PbTiO3 (PMN-PSn-PT) ferroelectric single ssingle crystals: (1) an absolute shifted P-E hystersis loops; (2) high piezoelectric coefficient d33 (1350 pC/N) for sample without undergoing any poling process; (3) no depolarization after high temperature (above Curie temperature) heat treatment. We call this unusual ferroelectric and piezoelectric response behavior as piezoelectric memory effect. A assumption theoretical model of piezoelectric memory effect induced by point defect was shown for understanding of piezoelectric memory effect in PMN-PSn-PT ferroelectric single crystals. Defect-dipoles were caused by point-defect generated in the crystals growth process. The driving force for spontaneous polarization and restoring force for temperature stability is provided by internal bias fields generated by long-range defect-dipoles. It is resulted that self-polarization state stable exists in PMN-PSn-PT ferroelectric single crystals. The physical mechanism of piezoelectric memory effect in PMN-PSn-PT ferroelectric single crystals is the target of this project. We will investigate several key basic issues, including structure, domain configuration, distribution and role of defects. The physical mechanism of piezoelectric memory effect induced by point-defect will be developed and improved by means of clarifying the relationship between structure, domain, point-defects and ferroelectric and piezoelectric response behavior. New method will be obtained for development of novel ferroelectric materials based on the physical mechanism.