Thermodynamic Properties of Layered Tetradymite-like Compounds of the Ag–Ge–Sb–Te System

The phase equilibria of the Ag–Ge–Sb–Te system in the part Ag₈GeTe₆–Ge–GeTe–Sb₂Te₃ were investigated by the electromotive force (EMF) method. The determined phase relations were used to express the chemical reactions. The potential-forming reactions were performed by applying electrochemical cells (−) C | Ag | Ag₂GeS₃-glass | D | C (+), where C is graphite, Ag₂GeS₃-glass is the fast purely Ag⁺ ions conducting electrolyte, and D is an equilibrium mixture of phases. According to the experimental data on the EMF versus temperature of each electrochemical cells, analytical equations for the Gibbs energies of GeSb₈Te₁₃, GeSb₆Te₁₀, GeSb₄Te₇, GeSb₂Te₄, Ge₂Sb₂Te₅, Ge₃Sb₂Te₆, and Ge₄Sb₂Te₇ compounds were obtained. The thermodynamic properties of silver-saturated tetradymite-like compounds have been calculated for the first time. A good correspondence between experimental values and structure data reported in the literature has been established.