二维材料压电和挠曲电效应的微观机理研究

Two-dimensional materials have many excellent mechanical and electrical properties beyond traditional materials. Thus, they attract extensive attention from mechanics, physics, and other fields. Because of their abundant electromechanical coupling effects (such as piezoelectric, flexoelectric, and tribo-piezoelectric effects), two-dimensional materials provide a good prospect for the development of a new generation of intelligent electronic devices. On the one hand, owing to their unique structural characteristics, two-dimensional materials exhibit novel electromechanical coupling properties that are not possessed by bulk materials, while little is known about its physical mechanism. On the other hand, the piezoelectric and flexoelectric effects are often difficult to be incorporated into the current theoretical framework. In this project, we study the piezoelectric and flexoelectric effects in two-dimensional materials. Using the first-principle method, the tight-binding method approximation, and the continuum model based on the interatomic potential, we mainly carry out the following study. Firstly, we try to uncover the microscopic mechanism of the piezoelectric and flexoelectric effects for two-dimensional materials and construct the analytical model. Then, we investigate the scaling behavior of piezoelectric and flexoelectric coefficients on thickness based on the developed model. Meanwhile, we analyze the effects of stacking mode and heterogeneous structure on the piezoelectric and flexoelectric properties of multilayer two-dimensional materials. This project will provide a theoretical guideline for the construction and development of new electromechanical coupling materials.

二维材料因具有超越传统材料的诸多优异力电性能，特别是其丰富的力电耦合维度（如压电，挠曲电，摩擦压电效应），为新一代智能电子器件的研发提供良好的前景，受到力学，物理，材料等多领域的广泛关注。一方面，得益于其独特的结构特征，二维材料往往呈现出体块材料不具备的奇异力电耦合性能，而人们对其深层机理知之甚少；另一方面，就其中存在的压电和挠曲电效应，往往难以纳入现有的理论框架。鉴于此，本项目以二维材料压电和挠曲电效应为研究对象，采用第一性原理、紧束缚近似、基于原子势函数连续统模型等方法，主要开展以下工作：探究二维材料压电和挠曲电效应的微观机理，构建解析的理论模型。基于发展出来的模型，探究二维材料的压电和挠曲电性随层数的变化规律，并归纳出压电和挠曲电系数关于厚度（层数）的标度行为。同时，分析多层二维材料的堆叠方式以及异质结构对压电和挠曲电性的影响。本项目为新型力电耦合材料的构建和性能开发提供理论指导。

低维材料压电效应的实验发现为下一代柔性智能电子器件的研发带来了良好的前景。本项目以二维材料为研究对象，对其压电和挠曲电性的微观机理进行初步研究，并将方法拓展至其它材料力学问题。首先，通过发展基于原子势函数连续统模型，利用紧束缚近似以及低能有效方法，结合第一性原理计算，构建了二维材料压电和弯曲电系数的解析模型。结果与DFT计算结果相当吻合，体现了模型的有效性。解析公式导出仅与体系原子的几个微观量有关，物理机理非常明确。此外，也研究了多层二维BN的压电性，结果表明其压电性与层数成反比，与实验观测结果相符。其次，我们也分析了二维sp2体系的反常压电现象，发现π电子的非平庸几何-拓扑性质是导致sp2晶体在相变点附近的压电响应突变现象的原因。基于这个结果，我们也研究了二维材料电子结构拓扑性质的多场调控，并开发了相应的原型器件，为二维材料器件化应用提供设计思路。最后，基于所发展的连续介质模型，我们对金刚石以及一些传统合金的强度进行理论预报。在项目的资助下，发表了6篇SCI期刊论文，协助团队培养研究生3名。项目结余数7.9436万元，剩余经费计划用于本项目研究后续支出。