多铁材料是同时具有两种或两种以上铁序（如铁电序、铁磁/反铁磁序和铁弹序）的新型功能材料，而BiFeO3是迄今为止发现的唯一在室温下具有铁电和铁磁性的单相多铁材料。特别是BiFeO3的掺杂改性，使其在铁序的起源和耦合机制等基础研究方面以及潜在的应用方面都表现出巨大的价值，成为多铁材料的研究模型，得到了人们广泛的关注。本项目拟利用X射线吸收谱和X射线衍射，结合多重散射从头计算和第一性原理计算等系统研究溶胶凝胶法制备BiFeO3的A位的稀土元素（La，Nd，Sm，Gd和Dy等）掺杂和B位的过渡金属元素（Mn，Cr，Co，Ni等）掺杂之后的结构及其稳定性。分析掺杂诱导纳米尺度区域结构相变的特点和形成机理，明确与掺杂元素种类和掺杂浓度的依赖关系，以及对铁序及耦合效应的影响，从新的视角探讨理解多铁材料BiFeO3的掺杂造成的铁序和耦合效应的变化的起因。

Multiferroic material is of new functional material simultaneously with two or more ferroic orders, such as ferroelectric order, ferromagnetic/antiferromagnetic order and ferroelastic order, and so far BiFeO3 is the only single-phase multiferroic material simultaneously with ferroelectric and ferromagnetic at room temperature. In particular, doped-BiFeO3, as a research model, has been widespread concern because it would modify the ferroic orders and coupling mechanism and has shown great value on the fundamental research as well as potential application. This project intends, using the X-ray absorption spectroscopy and X-ray diffraction, combined with multiple scattering ab initio calculation and first principle calculation, etc., to investigate systematically the structure and its stability of BiFeO3 doped by REE (La, Nd, Sm, Gd, and Dy, etc.) at site-A and by transition metal elements ( Mn, Cr, Co, and Ni, etc.) at site-B, fabricated by sol-gel method. We will analyze the characteristics and formation mechanism of doping-induced structural phase transition of nanoscale region, and will clarify the dependence of doping element type and doping concentration, as well as the impact on ferroic orders and coupling effects. The results will provide a new perspective to understand the origin and changes of ferroic orders and coupling effects caused by doped BiFeO3.