先进多功能材料中挠曲电效应的基础理论及定量表征方法研究

The flexoelectricity in advanced multifunctional materials is a novel electromechanical coupling effect between strain gradient and polarization, which is frontier multidisciplinary research area. It is difficult to extend available strain/stress-based electromechanical coupling theory and methodology to flexoelectricity, due to the higher order effect of the strain gradient. Furthermore, the current theory, computational method and measurement are not capable of describing the full flexoelectric coefficient tensor quantitatively, which is the key issue in flexoelectricity. Based on our preliminary research in flexoelectricity, we propose to (i) establish an atomic-level theory to describe the relationship between the microscopic structure and flexoelectric coefficient by choosing the change of electric current density as a fundamental variable; (ii) develop an effective first-principles method to calculate the full flexoelectric coefficient tensor for multifunctional materials; (iii) measure the full flexoelectric tensor by combining the first-principles calculations, bending measurements and the compressing measurement with varying cross section of the samples. It is expected that an atomic-level theory and quantitative characterization methods for flexoelectric coefficient will be obtained, which will be the basis for the development of flexoelectricity and its applications.

先进多功能材料中的挠曲电效应，是一种新颖的应变梯度与电学量之间的力电耦合效应，是多学科交叉的前沿研究。应变梯度的引入使得基于应变/应力的力电耦合理论和方法不能直接用于挠曲电理论。目前的挠曲电理论、模拟计算以及测量表征方法都难以对挠曲电效应中关键和核心的力电耦合系数进行完整定量表征和描述，迫切需要发展全新的理论和方法对其进行研究。本项目在前期研究的基础上，围绕挠曲电效应系数这个核心关键问题，拟（1）采取全新的电流密度改变量为基本量，从原子尺度建立材料微结构与挠曲电效应系数之间的理论模型；（2）基于建立的微观理论，发展高效的模拟计算方法，对常见多功能材料的挠曲电系数张量进行第一性原理计算；（3）结合理论计算结果，联合弯曲实验和变截面压缩实验，测量完整挠曲电效应系数张量。本项目期望在挠曲电微观理论和实验定量表征方面获得原创性成果，为挠曲电效应学科发展与工程实际应用提供指导。

挠曲电效应是一种新型的力电耦合效应，反映的是材料中应变梯度与电极化强度之间的线性耦合关系，在微纳尺度下对材料性能有着重要影响。通过本项目的实施，我们建立了纳米尺度下挠曲电效应的理论模型并获得了解析解，揭示了挠曲电效应对材料力学性能的影响，基于此提出了排除压电效应的挠曲电系数测试方法，采用第一性原理计算揭示了挠曲电效应对电子器件性能调控的微观机制，为挠曲电效应的定量表征以及器件应用奠定了基础。