基于价电子密度对R5X4体系的一级磁相变调控和新相探索的研究

本项目利用价电子密度作为R5X4（R=稀土元素，X=主族元素）体系一级磁相变的调控手段和新相探索的依据。对于一级磁相变的调控，我们拟改变Gd5SixGe4-x的价电子密度，降低滞后效应，增强低磁场下的磁熵变、磁电阻等效应。对于新相探索，基于R5X4相存在的价电子密度范围，设计出不含碳族元素的新相，例如R5TrxPn4-x（Tr=Al, Ga, In；Pn=P, Sb, Bi）、R5TrxQ4-x（Q=S, Se, Te）。利用第一原理计算论证设计材料的结构稳定性和预测其物理性能。实验上，采用多种固态合成方法（高温固相反应、电弧熔炼、高频感应加热、金属溶剂、化学气相传输等）制备所需材料。运用XRD、SEM-EDS、PPMS等手段研究晶体结构、成分，探索发现半金属性等新的物理性能。结合实验和理论结果，阐明晶体结构-成键-性能之间的本质关系，为稀土磁相变材料的性能优化和新相探索提供新的思路。

This project is to tune first-order magnetostructural transitions and to explore novel phases of R5X4 (R=rare-earth atoms, X=main-group atoms) system through valence electron concentration (VEC). For manipulation of first-order magnetostructural transitions, we aim to decrease the magnetic hysteresis effect of Gd5SixGe4-x and to enhance its magnetocaloric and magnetoresistance effects in low magnetic field by adjusting VEC. For exploration of new phases, the non-tetrelide-containing R5X4 compounds, such as R5TrxPn4-x (Tr=Al, Ga, In；Pn=P, Sb, Bi), R5TrxQ4-x (Q=S, Se, Te), can be designed based on the VEC range in which the R5X4 phases survive. The structural stability and physical properties of designed compounds will be verified by employing first-principles calculations. Experimentally, the targeted materials are attempted to prepare by multiple solid-state synthesis methods, such as high-temperature solid-state reaction, arc melting, high-frequency induction heating, metal flux, chemical vapor transport and so on. The crystal structures, composition and novel physical properties (e.g., half metal) will be investigated by using XRD, SEM-EDS, PPMS etc. The theoretical and experimental data will be combined to be analyzed to illustrate the structure-bond-property relationship, paving a new route to property optimization and searching for new phases of rare-earth-based magnetostructural transition materials.