纳尺度铁电材料中挠曲电效应的相场法研究

Flexoelectricity describes the induction of electric polarization with strain gradient. Due to the property of size dependence, flexoelectricity will significantly influence the properties of nanoscale ferroelectrics. In the proposed project, we will focus on nanoscale ferroelectrics and utilize phase field method to study the influence of flexoelectricity on the effective piezoelectricity and the polarization switching behaviors. First, the phase field model suitable for single phase ferroelectrics will be established with taking into consideration all the important factors, such as electrostatic field, polarization gradient term, electrostrictive effect, flexoelectric effect and so on. Then, the model is extended to simulate the two-phase composite system by incorporating the elastic and dielectric inhomogeneity. The influence of components size and volume ratio can be thoroughly studied based on the proposed model. Finally, by incorporating the mechanical boundary condition imposed with the tip of atomic force microscopic, the mechanism of 180 degree switching of polarization in epitaxial ferroelectric thin film will be studied. Under the general trend of device miniaturization, the influence of flexoelectricity will be more and more important with the continue shrinkage of material size. The proposed project will be helpful for further understanding the mechanism of flexoelectricity and provides theoretical supports for improving material performance.

挠曲电效应描述了应变梯度产生电极化的物理现象。因为其所具有的尺寸相关性，挠曲电效应对纳尺度铁电材料性质的影响将非常显著。本项目拟以纳尺度铁电材料为研究对象，基于相场方法研究挠曲电效应对铁电材料等效压电性能以及极化反转行为的影响。首先，在充分考虑静电场、极化梯度场、电致伸缩效应、挠曲电效应等影响因素的基础上，针对单相铁电材料构建相应的相场模型；然后，引入弹性非均匀性以及介电非均匀性，使模型适用于两相复合材料问题，进而研究材料尺寸、组分比等因素对复合材料等效压电性能的影响；最后，基于建立的模型结合原子力探针施加的力学边界条件研究外延生长铁电薄膜中力学手段180度反转电极化的机制。当今社会，设备小型化是一个大的发展趋势，而挠曲电效应的影响随着材料尺寸减小将变得越来越重要。本项目的研究工作将有助于深入理解挠曲电效应的作用机理，并为优化材料性能提供理论依据。