Phase equilibra in the Ag2S–Ag8GeS6–Ag8SiS6 system and some properties of solid solutions

Abstract

Phase equilibria in the Ag2S–Ag8SiS6–Ag8GeS6 system were studied using differential thermal analysis and powder X-ray diffraction technique. Boundary section Ag8SiS6 – Ag8GeS6, liquidus surface projection, an isothermal section of the phase diagram at 300 K, and some polythermal sections of the studied system were constructed. The formation of continuous series of solid solutions between both crystalline modifications of the starting compounds was determined in the Ag8SiS6–Ag8GeS6 system. The liquidus surface of the Ag2S–Ag8SiS6–Ag8GeS6 system consists of two fields corresponding to the primary crystallization of the high-temperature modifications of the HT-Ag8Si1-xGexS6 and HTAg 2S phases. Lattice parameters for both modification of solid solutions were calculated based on powder X-ray diffraction data. The concentration dependence of lattice parameters obeys Vegard’s rule. The obtained new phases are of interest as environmentally safe materials with thermoelectric properties and mixed ionelectron conductivity

Keywords

• argyrodite family compounds
• silver-germanium sulfide
• silver-silicon sulfide
• phase equilibria
• solid solutions
• t-x diagram
• crystal structure