具有金刚石结构的碱金属基I2-II-IV-VI4型四元硫属化合物的新相探索与物性研究

本项目利用碱金属无d电子的特性，设计和探索合成具有金刚石结构的I2-II-IV-VI4（I=碱金属，VI=S, Se, Te）型硫属化合物，有望成为新型的中远红外非线性光学材料和铁磁半导体。对于非线性光学材料，II族元素为s区的Mg、Ca和深d电子能级的Zn、Cd等原子，这类化合物具有不含贵金属Ag、大的二次谐波产生效应、宽禁带等优点。当II族为Cr-Ni、Eu等磁性元素时，在I2-II-IV-VI4中有望发现新的磁性半导体体系，展现新奇性能。实验上，采用多种固态合成方法（助熔剂法、溶剂热合成、高温固相反应、化学气相传输等）制备目标体系。运用XRD、SEM-EDS、UV-Vis-NIR光谱、Kurtz-NLO系统、PPMS等手段研究结构、成分、能隙、二次谐波产生等性能。结合实验和第一性原理计算探讨结构的稳定性。四元硫属化合物体系中多种阳离子的组合，为材料设计提供了充分的成分和结构自由度。

This project is to design and subsequent to explore novel phases of quaternary I2-II-IV-VI4 (I=alkali metal atoms, VI=S, Se, Te) chalcogenides with diamond-like structures, based on the octet rule and energy band engineering. Due to the non-d-electron nature of the alkali metal atoms, the quaternary chalcogenides are expected to be promising mid-IR nonlinear optical (NLO) materials and ferromagnetic semiconductors. For the design of NLO materials, II is postulated to be occupied by the s elements, e.g., Mg and Ca, or Zn/Cd atoms with deep d-level, therefore, those quaternaries offer the unique properties, such as Ag-free constituent, large second harmonic generation (SHG) and wide band gap, etc. In the case of II=Cr-Ni and Eu, the introduce of magnetic atoms lead to the quaternary chalcogenides as new ferromagnetic semiconductors, in which novel physics properties are to be investigated. The targeted materials will be prepared by using synthetic strategies, e.g., polychalcogenide flux, solvothermal reaction, high-temperature solid-state synthesis, chemical vapor transport. The crystal structures, chemical composition, band gap and SHG response will be systematically studied by XRD, SEM-EDS, UV-Vis-NIR spectroscopy, Kurtz-NLO system and PPMS. The stability of possible structures will be discussed by a combination of experimental results and first-principles calculations. The quaternary diamond-like semiconductors provide an excellent opportunity for new phase exploration and physical tuning due to the compositional and structural flexibility.