铁电功能材料具有极化翻转、力电耦合和光电等效应，是微纳电子器件中的重要组元。其中弛豫铁电单晶因其特有的巨压电效应，在军事及民用领域具有特殊应用。研究发现，多相共存、共存区的单斜相以及畴界是巨压电效应的主要影响因素。由于铁电相和畴结构与弹性力场密切相关，构建恰当的弹性力场获得精细微纳畴结构对进一步提高压电响应至关重要，但目前尚缺乏对精细铁电畴的深入研究。本项目拟针对弛豫铁电单晶，研究其相变规律和临界特征行为，提出朗道自由能系数的提取方法，建立基于能量竞争的弛豫铁电单晶唯象理论；研究共存相、微畴间的弹性力场及畸变相的特性，建立微纳畴结构与性能的构效关系；基于共存相的竞争机制，通过畴工程调控畴结构及晶体内的弹性力场，实现人工可控精细畴结构，并研究其在外场下的动态响应规律，揭示小场下灵敏压电响应的机理。本研究将为新型压电材料的设计提供新的途径，并为多元共存体系的微畴结构设计及性能调控提供研究基础。

Ferroelectric materials, with polarization, electromechanical and electro-optic coupling effects, are one of the most important functional elements and widely used in micro/nano devices. Relaxor-ferroelectric single crystals have excellent piezoelectric property and are considered as important materials in many fields. Since monoclinic phases, domain structures and domain walls are crucial for ultrahigh piezoelectricity, especially, the adaptive phases are highly related with the elastic filed around the phase interfaces, it is thus necessary to build nano domain structures with rich domain walls and monoclinic phases for higher piezoelectric properties. In this project, we will focus on the relaxor-ferroelectric single crystals and study the free energies of coexisting phases and internal elastic field in the framework of the Landau phenomenological theory aiming to find the correlation of physical properties and corresponding domain structures. Based on the phase competition, the coexisting domain structures could be adjusted into nano size by the external electric field, elastic field and temperature. We will focus on the formation of nano-sized domains, the effect of nonlinear elastic field, and phases in the domain walls and their physical properties. Dynamic responses of the domain structure to external stimuli will also be studied aiming to find large piezoelectric response under small stimuli. The results will provide route for new piezoelectric materials and fundamental data for the formation of nanodomains in phase coexisting systems.