铁电畴结构的X射线衍射成像与关联相场模型重构研究

随着同步辐射光源及线站仪器的发展，X射线衍射成像技术在过去十多年间取得多个根本性革新。该技术具有体探测灵敏性、易于原位操作性及可高度定量化分析等诸多优势，在材料介观尺度晶体结构表征方面展现出重大应用潜力。本项目拟采用X射线衍射成像研究几类典型铁电材料体系（例如BiFeO3岛状纳米结构与外延薄膜、Pb(Zr,Ti)O3陶瓷）的畴结构组态及其在原位电场、压力与变温环境下的动态响应过程。在实验研究基础上，本项目将发展一种全新的分析方法：基于关联相场模型对X射线衍射图像匹配拟合与逆向重构。该方法的实施关键是大规模三维铁电相场模型的建立及其X射线运动学衍射衬度的高真实度模拟。该方法将跨越基于层析成像等算法的传统实验数据重构过程，实现从数据到物理模型的直接关联，从而可深入揭示铁电材料中畴结构与物性之间的关系。本项目将实现X射线成像研究方法的一个重要突破，同时为相关线站仪器在国内的发展提供策略。

During the last decade, X-ray diffraction imaging (XDM) techniques have been fundamentally innovated following the development in synchrotron X-ray sources and beamline instrumentations. XDM offers many advantages including high bulk sensitivity, in-situ operation capability and quantitativeness, and as such, has demonstrated significant application potentials in the characterizations of crystal structure of materials at mesoscales. This project aims to investigate several typical ferroelectric materials systems (such as BiFeO3 island-like nanostructures and epitaxial thin films and Pb(Zr,Ti)O3 ceramics) using XDM, with an emphasis on the domain configurations and their dynamical response to in-situ applied electric field, mechanical stress and varying temperature. On the basis of experimental observations, we will further develop a novel analysis method, that is, matching and inverse reconstruction of XDM images based on correlative phase-field models. The keys to implementing this method are establishment of large-scale, three dimensional ferroelectric phase-field modeling and high-veracity simulation of the X-ray kinematical diffraction contrast of the latter models. This method will circumvent the traditional reconstruction process of experimental data using tomography and other algorithms, and build a direct link between the data and physics-based models, thereby thoroughly revealing the relationship between the domain structure and physical properties of ferroelectric materials. The fulfilment of this project will not only embody a major breakthrough in the X-ray diffraction imaging methodology, but also can provide strategic advice for the development of XDM beamline instruments in China.