弛豫铁电体中基于共存相的精细弹性畴调控机理及性能研究

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.

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。

弛豫铁电单晶因压电系数高、损耗低、驱动电场小等特点，被广泛用于传感、驱动等元器件。由于驰豫铁电体相结构复杂，存在多相共存及单斜相，因此复杂的畴界应力及应力导致的畸变相与材料性能息息相关，理解其相界弹性力场耦合机制，从而进行有效微畴结构设计是进一步提高压电响应的关键。本项目针对巨压电材料铌镁酸铅铁电单晶系数的缺失，建立了驰豫型铁电单晶的朗道系数提取方法，获得了四方相、三方相及相界处组份的朗道自由能展开系数，并采用机器学习方法辅助系数提取，为实现自动化能量提取建立了一种快捷方式，总结了单晶中影响畴尺寸的控制条件及微畴结构与宏观物理性能的构效关系。基于临界态进行物理性能调控原理，提出铁电单晶共存相理论与畴结构的全角度偏光研究方法，并采用机器学习方法建立了快速识别畴结构与相结构的深度学习方法，大大提高晶体畴的研究准确性与晶体缺陷检测速度。基于共存态的临界竞争机制，通过引入应力条件，通过优化弛豫铁电单晶精细畴结构实验技术，调控具有协同翻转效应的畴结构，精准调控铁电极化指向，形成109度畴占优状态，大大提高了压电性能并提高了晶体的透明性。同时，晶体的畴尺寸。研究结果发表在Nature Communications、Physical Review B、Applied physics Letter、Ceramic International等国际期刊上，为新型压电材料及多场耦合异质结构提供研究基础，并为低能耗、高性能传感驱动器件的大规模应用奠定了理论和实验基础。