Electrochemical Study of Thermodynamic Properties of the Ag8SnS6 Compound

Equilibrium alloys of the Ag–Sn–S system in the Ag2S–SnS2–S composition range are studied by electromotive forces (EMF) measurements of concentration cells relative to a silver electrode cell with Ag4RbI5 solid electrolyte over the 300–390 K temperature range. A linear equation for the EMF temperature dependence is obtained, from which the silver partial molar functions in the alloys are calculated. Based on the solid-phase equilibria diagram of the Ag–Sn–S system, a virtual potential-determining reaction is established. This reaction is used in the calculating of the standard thermodynamic formation functions and standard entropy of the Ag8SnS6 low-temperature modification. By combining the obtained data with the phase transition thermodynamic functions of the compound, the corresponding functions for its high-temperature modification are calculated.