点缺陷诱导PMN-PSn-PT铁电单晶压电记忆效应机理的关键基础问题

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.

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。

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）单晶在未极化的情况下具有高的压电系数，部分样品的压电系数d33高于1000 pC/N；（3）在高于居里温度（TC）的温度热处理后，压电系数没有下降，没有出现退极化，表现为一种压电记忆效应。研究PMN-PSn-PT铁电单晶的压电记忆效应和其结构、电畴、点缺陷的关系，阐明压电记忆效应的的结构来源及其物理本质，对开发新材料具有指导意义。本项目的主要研究内容包括以下几个部分：（1）生长了不同组分的PMN-PSn-PT铁电单晶，便于研究压电记忆效应和组分、缺陷浓度的关系；（2）采用XRD和偏光显微镜对PMN-PSn-PT铁电单晶的结构进行了研究；（3）采用偏光显微镜和压电力显微镜对PMN-PSn-PT铁电单晶的畴结构进行了研究；（4）氧空位等缺陷的表征；（5）分析缺陷偶极子的长程有序行为，压电记忆效应的机理分析。研究结果表明在PMN-PSn-PT铁电单晶中缺陷极化对异常的铁电压电响应行为起了主要作用。缺陷极化的作用主要是对自发极化提供一种驱动力和回复力，导致了自极化性能和压电性能的高温度稳定性。这对开发新材料具有指导意义。