通过形变孪晶大幅度提高铁电材料力电耦合性能：多尺度机理分析和实验验证

The electromechanical coupling properties of ferroelectric materials are determined by domain switching, while the domain switching is depended on the type number of variants and the compatibility of transformation strain and spontaneous polarization among them. The coexistence of multiple variants can be achieved through morphotropic phase boundaries, but the limited systems with morphotropic phase boundaries are discovered, leading to the enhancement of electromechanical coupling and applications of common ferroelectric materials difficult. In order to overcome this problem, we will develop a universal alternative to the coexistence of multiple variants for enhancing electromechanical coupling in ferroelectrics using mechanical twin engineering, where mechanical twins are formed above Curie temperature under mechanical loading, and more types of ferroelectric variants are induced after ferroelectrics cooled, which are motived by our recent experimental observations. Combining the mesoscopic mechanic analyses and phase-field simulations, we will analyze the compatibility of transformation strain and spontaneous polarization, switchable of ferroelectric domains, microstructures, and effective macroscopic electromechanical properties of mechanical twin engineering ferroelectrics. All of those will allow us to unravel the multiscale mechanisms of mechanical twin engineering ferroelectrics. Additionally, we will realize the coexistence of multiple variants in polycrystalline ferroelectric films using mechanical twin engineering from experimentation side. The proposed method can enhance the electromechanical properties and work for any ferroelectric material systems, resulting in more ferroelectrics used in commercial applications.

铁电材料力电耦合性能优劣在很大程度上取决于其电畴翻转难易程度，而电畴翻转难易则取决于其铁电变体种类数量和变体之间的力电匹配性。通过准同型相界可以实现多种铁电变体共存，但具有准同型相界的铁电材料非常少，限制了普通铁电材料力电性能的提高和应用。为克服这一困难，并受最近初步预研实验结果启发，我们提出通过机械加载在铁电材料居里温度以上形成形变孪晶，材料降温相变后能大幅度增加铁电变体种类数量，从而提高其力电耦合性能。我们将结合细观力学分析和相场模拟，从形变孪晶化后多种铁电变体共存的力电匹配、电畴易极化翻转能力、微观结构、有效宏观力电性能四个方面，深刻揭示形变孪晶提高力电耦合性能的多尺度机理，并以此为基础，进行实验验证。该方法对一般铁电材料普遍适用，能大幅度提高其力电耦合性能，从而推动更多铁电材料的应用。

增强铁电材料力电性能是铁电材料广泛应用的关键。基于细观力学、相场模拟、热力学理论的多尺度理论计算模拟分析，提出了通过剪切形变可以在普通铁电材料中诱导出孪晶结构，实现多种变体共存，理论预测孪晶结构的出现能够提升铁电材料力电性能，为铁电材料力电性能的提升指引了路径。对孪晶化后铁电变体进行了力电匹配分析、微观结构模拟、电畴翻转能力模拟，并将细观力学自洽模型推广用于含孪晶的铁电材料的宏观力电性能预测之中，理论结果显示孪晶化后铁电材料的宏观力电性能得到了增强，其机理源于多变体共存。发展了局域力电耦合表征分析方法，为探测铁电材料局域力电耦合性能提供了局域表征及其分析手段。在普通铁电材料钛酸钡中，实验上制备出了含孪晶结构的钛酸钡薄膜和钛酸钡粉，证实了铁电材料孪晶结构的存在，并实验上发现孪晶结构的出现提升了钛酸钡铁电材料力电性能。研究工作提出了在铁电材料中形成孪晶结构的方法，为具有孪晶结构铁电材料的理论分析和实验表征提供了手段，指引了一种提升铁电材料力电性能的方法。目前已在Science China Technological Sciences、Nano Energy、Nanotechnology等上发表SCI论文18篇，申请发明专利2项，获得软件著作权1项。

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