有机-无机杂化钙钛矿化合物（MAPbX3）的挠曲电行为研究

Flexoelectric effect has recently exhibited important application potential in many micro/nano materials due to its absence of symmetry constraint and distinctive size effect. However, the present flexoelectric materials have relatively poor flexoelectric performance, resulting in its real application difficult. CH3NH3PbX3 (MA= CH3NH3, X=Br、Cl、I), as one of the representative of hybrid inorganic-organic perovskites, both contains the perovskite framework and polar molecules just like the liquid crystal, are possible to be good flexoelectric candidates. The early stage work of this proposal has confirmed that the flexoelectric performance of MAPbI3 is one order higher than the previous best flexoelectric material barium strontium titanate, but the mechanism is much less understood. This proposal mainly uses molecules dynamics and atomic characterization method to study the tuning mechanism of strain gradient for the lattice, and uses preparation optimization and halide element tuning to explore the superior flexoelectric materials. This proposal will provide more interpretation regarding the mechanism of enhanced flexoelectric material and provide experimental and theoretical guideline for the further development of flexoelectric materials.

挠曲电效应因具有不受对称性限制和尺寸效应等优点而在微纳米材料中具有重要的应用潜质，但已知的材料挠曲电性能较弱，达不到实用标准。有机-无机杂化钙钛矿材料典型体系MAPbX3 (MA=CH3NH3，X=Br、Cl、I)既有钙钛矿结构的基本骨架，又嵌含类似液晶材料的有机极性分子，兼具两类挠曲电材料的特征，有成为增强挠曲电材料的潜质。我们通过项目准备已在实验上测到MAPbI3材料挠曲电系数比目前公认最好的钛酸锶钡材料有数量级提升。但目前对其增强挠曲电来源尚不清楚。本项目主要通过运用分子动力学和原位表征方法研究应变梯度对MAPbX3极性基团和晶格的调控机理；并通过实验工艺优化和卤族元素的成分调控，以期开发性能更为优良的挠曲电材料，并为深入理解挠曲电性能的增强机理以及为挠曲电理论发展和后续相关扰曲电材料体系的开发提供参考。

挠曲电效应因具有不受对称性限制和尺寸效应等优点而在微纳米材料中具有重要的应用潜质，但已知的材料挠曲电性能较弱，达不到实用标准。有机-无机杂化钙钛矿材料典型体系MAPbX3 (MA=CH3NH3，X=Br、Cl、I)既有钙钛矿结构的基本骨架，又嵌含类似液晶材料的有机极性分子，兼具两类挠曲电材料的特征，有成为增强挠曲电材料的潜质。.项目组采用逆温结晶法成功制备高稳定性、可用于挠曲电性能测量的有机-无机杂化钙钛矿MAPbX3单晶材料。通过系统研究发现，MAPbX3材料的挠曲电系数可达到30 µC/m，相比以往金属氧化物材料体系有4-5个数量级的提升。此外，本项目揭示出MAPbX3单晶具有显著的挠曲电尺寸效应和明显的电极依赖性，这两点实验证据充分表明，MAPbX3单晶的巨大挠曲电性起源于半导体势垒效应。本项目进一步发展了一套系统的半导体耗尽层贡献挠曲电极化的新型理论，相关研究成果可为学术界深入理解挠曲电性能的增强机理以及为挠曲电理论发展和后续相关扰曲电材料体系和器件的开发提供参考。