新型非常规铁电体中铁电畴壁的第一性原理研究

Ferroelectric domain structures and domain walls widely exist in low-dimensional ferroelectric materials. They not only possess a rich variety of novel physical properties, but also can make an essential difference on the properties of parent materials and thus enrich the methods of device regulation. Along with the miniaturization of electronic multi-functional devices and the increasing importance of low-dimensional materials, it is highly required to thoroughly understand the formation of domain wall, the influence of domain walls on parent structures and the response to the external field as means of regulation. Meanwhile, various kinds of improper ferroelectrics have been the focus of research for the possibility of realizing room-temperature multiferroicity. Therefore, improper ferroelectrics provide a versatile platform for the investigation of ferroelectric domain walls. In this project, we will explore the nature of ferroelectric domain walls using first-principles calculations, aiming at providing a systematical investigation on the mechanical, electric and response properties of ferroelectric domain walls in different types of ferroelectrics. We mainly focus on the three physical problems: The microstructure, formation and response to external field of charged domain walls; epitaxial strain effect on ferroelectric domain walls; and magnetoelectric coupling at domain walls. On the basis of our studies, we hope to promote the design of newtype functional ferroelectric devices and make a breakthrough in both fundamental physical problems and industry of future functional devices.

低维铁电材料中存在着丰富的畴壁结构，它们不仅自身有着新颖的物理性质，更能够影响材料的外场响应，从而丰富器件调控的手段。随着器件的小型化，低维材料日益重要，迫切需要透彻理解各种畴壁的生长机制、外场响应及对母体性质的影响；同时，非常规铁电材料由于其具有实现室温多铁的潜力，为上述研究提供了有效的平台。本项目拟通过第一性原理计算，在多种铁电材料中，综合系统地研究各种类型的铁电畴壁的静电效应、力学效应、磁电耦合机制等，力图阐明带电畴壁的形成过程和能量，揭示外延应变对畴壁的影响规律和微观作用，并理解多铁中铁电畴壁处的磁电耦合效应。在此基础上，将畴壁作为一个新的调控自由度，提出在非常规铁电体中有目的性地获得更优良性能的设计方案，以实现基础问题研究、新材料与器件设计中的突破。

随着器件的小型化，低维功能材料日益获得关注，其中铁电材料及同时具有铁电及磁性的多铁材料是研究的热点之一。本项目在对低维铁电材料和非常规六角几何铁电体进行大量文献调研的基础上，通过第一性原理计算，研究了低维铁电体的多铁性及磁电耦合性质和六角铁电材料的电荷序畴与铁电畴的相互作用。项目研究了实验观测的LuFe2O4中的孪畴结构，发现LuFe2O4中包含的LuFeO3是LuFe2O4电荷序的畴壁，而LuFe2O4单层在LuFeO3中也可以成为铁电畴壁。项目发现了一种新型二维多铁材料VOX2 (X=Cl, Br, I)，该材料集合了第一类多铁和第二类多铁的优点，既有相当大的铁电极化，又有一定程度的磁电耦合，是一种很有潜力的多铁器件材料。本项目还对近期的六角铁酸、锰酸物中的铁电、多铁及畴壁作用的相关工作进行了归纳整理，有助于该领域的发展。通过本项目的实施，我们发现了六角铁酸物的电荷序和铁电性的规律，预测了一类集强铁电性和磁电耦合于一体的二维多铁材料，对基础问题研究和新型功能材料的发现具有十分积极的作用。