THE CHARACTERISTICS OF THE CRYSTAL STRUCTURE OF THE AG(СU)2CDHF3S8 SULFIDES

Abstract

The work has been devoted to study the peculiarities of the crystal structure of the Ag(Cu)2CdHf3S8 new quaternary sulfides as prospective materials that may belong to the stuff with low thermal conductivity. The synthesis of samples has been conducted in quartz vacuumed (10- 2 Pa) ampoules in muffle furnace with software control of technological processes. The semiconductor-pure elements were used for obtaining samples. In order to study phase composition and determine the crystal structure of the obtained samples, we have recorded diffractograms of the samples using DRON 4-13. The crustal structure was determined with using Ritveld’s method. Further, it has been visualized with VESTA program. The crystal structure of the obtained samples belongs to the MgAl2O4 structure type (SG Fd-3m, Pearson symbol cF56) with cubic symmetry. The structure of these compounds is based on the three-layer close packing of sulfur atoms in which the voids are filled with Ag, Cu, Cd i Hf atoms. Moreover, the tetrahedral voids are packed to 1/8, and the octahedral voids – to ½. The mix [Cd:Hf] (~1:3) is located in the site 16d and has octahedral surrounding with S atoms and Ag (Cu) atoms fill the tetrahedral site 8a formed by four S atoms. To transit from the Ag2CdHf3S8 crystal structure to Cu2CdHf3S8, the lattice parameters decrease due to the decrease in the atomic radius of Cu, which causes an increase in distortion in the octahedral environment. At the same time, the volume of the tetrahedron increases proportionally without causing distortion in the polyhedron. In general, the crystal structure of Ag(Cu)2CdHf3S8 sulfides indicates that the phases are interesting and promising, as they contain the transition metal Cd and the f-element Hf, which can significantly change their functionality.