混合价态诱发Nd-Ce-Fe-B磁体主相晶胞参数c离散机制研究

It has become a popular topic to prepare Nd-Ce-Fe-B magnets with high abundance rare earth Ce instead of Pr and Nd. In recent years, some studies have found that the magnetic coercivity abnormal improvement in specific Ce content (20 wt.%), and its value is better than Nd-Fe-B magnet without Ce addition. Through the preliminary research, it was found that the cell parameter c of the RE2Fe14B main phase in the magnet is discrete when the amount of Ce is 20 wt.%, and the magnetic domain pinning center is formed by the defects such as cell mismatch, so that the coercivity is promoted. However, the cell parameter c discrete mechanism of the main phase is still lack of effective analysis. Therefore, this project uses synchrotron radiation X - ray absorption fine structure to determine the valence state, mixing ratio and site preference of Ce in the cell. Combined with the results of the first-principles calculations, the binding energy of solid solution substitution and the cell parameters of Ce with different types at various crystal sites are to be obtained. It is systematically to investigate the evolution of the valence state and the thermodynamic process of solid solution substitution via experimental measurements and theoretical modeling. The relationship between Ce content, valence mixing ratio, sites preference and cell parameters is to be analysed in order to find the cell parameter c discrete mechanism of main phase when the Ce was added 20 wt.%, which is provide theoretical and experimental guidance for preparation of high performance Nd-Ce-Fe-B rare earth permanent magnets.

采用高丰度稀土Ce替代Pr、Nd制备Nd-Ce-Fe-B磁体已成为当前研究热点，近来有结果表明Ce添加量20wt.%附近磁体矫顽力异常提升，其数值优于未添加Ce的Nd-Fe-B磁体。经前期研究发现，Ce添加量20wt.%时磁体RE2Fe14B主相晶胞参数c呈离散变化，并凭借晶胞错配等缺陷形成磁畴钉扎中心，使矫顽力提升，但对主相晶胞参数c离散形成机制尚缺乏有效解析。因此，本项目采用同步辐射X射线吸收精细结构测定Ce在晶胞中价态、混合比率及择优代位情况，结合第一性原理计算获取不同类型Ce在各晶位固溶取代结合能及晶胞参数相关信息，从实验测定与理论计算两方面，系统研究Ce取代时价态演化规律及固溶取代热力学过程，构建Ce添加量、价态混合比率、择优代位与晶胞参数的映射规律，揭示Ce添加量20wt.%时主相晶胞参数c离散机制，为调控制备高性能Nd-Ce-Fe-B稀土永磁材料提供理论与实验新思路。

采用高丰度稀土Ce替代Pr、Nd制备Nd-Ce-Fe-B磁体已经成为当前研究的热点，但高丰度稀土所构建磁体的RE2Fe14B主相内禀性能偏低，微观结构较差，导致磁体综合性能不尽如人意。本项目基于前期特定Ce添加量下Nd-Ce-Fe-B磁体矫顽力异常提升行为相关研究，通过同步辐射X射线吸收精细谱、X射线光电子能谱等精确测定了Ce在晶胞中价态、混合比率以及择优代位情况。结合第一性原理计算获取了不同类型的Ce在固溶取代过程中结合能及对应晶胞结构变化情况。理论与实践相互验证，揭示了Ce在特定添加量下矫顽力异常提升机理，明确了晶胞参数c离散形成机制。主要研究内容和重要成果有：（1）同步辐射技术测定了不同Ce添加量下磁体的价态信息，当含量达20 wt.%时，Ce3+比例高达72.45%，矫顽力增高。（2）第一性原理计算不同类型Ce 固溶取代结合能及晶胞参数变化情况，当2个Ce原子掺杂时c 轴的离散程度最大(0.0415 Å)。（3）基于模拟和实测数据，晶格参数离散变化导致主相间晶格失配，产生较大内应力和主相散射应力场，依托该处较高的畴壁能可阻碍畴壁运动，从而产生高矫顽力。项目对于制备高性价比的优质稀土永磁材料，解决高丰度稀土资源供需不平衡现象具有重要意义。