CRYSTAL GROWTH OF Ag8SiS6

Abstract

Compounds with high ionic conductivity in the solid state, the so-called superionics, are of considerable interest. This scientific interest is driven by the ever-increasing demand for electrochemical energy storage. Promising superionic compounds include argyrodites, complex chalcogenides formed on the basis of two types of cations. This paper presents the results of studies on the growth of Ag8SiS6 single crystal. The growth of Ag8SiS6 single crystals was carried out in two stages. The first stage involved the synthesis of a polycrystalline Ag8SiS6 alloy by fusing high-purity elemental components in vacuum (0.13 Pa) quartz ampoules. The single-phase nature of the synthesized alloy was confirmed by XRD. The results of thermal analysis confirmed the congruent nature of the melting of Ag8SiS6 (Tmelt = 965°C) and the presence of polymorphism (Tpolim = 240°C). The single crystal of Ag8SiS6 was obtained by directed crystallization from the melt. The growth regime of Ag8SiS6 was developed taking into account the results of thermal analysis. The grown single crystal of Ag8SiS6 is ~30 mm long and 12 mm in diameter. The single crystallinity of the grown sample was determined by XRD. According to the XRD results, it was found that the grown Ag8SiS6 single crystal crystallizes in the low-temperature modification of SPG Pna21 with lattice parameters: a = 15.06 Å, b = 7.44 Å, c = 10.54 Å.