THERMODYNAMIC PROPERTIES OF SOME TERNARY COMPOUNDS OF THE ARGYRODITE FAMILY

Abstract

Compounds of the argyrodite family are valuable environmentally friendly functional materials with mixed ion-electronic conductivity, thermoelectric, photovoltaic, optical, and other properties. This paper presents the results of a thermodynamic study of the Cu8GeS6 and Cu8GeSe6 compounds - representatives of this family using the EMF method with Cu4RbCl3I2 solid electrolyte in the 295-430 K temperature range. From the EMF measurement data, the partial molar functions of copper were calculated in both crystal modifications of the Cu8GeS6 and Cu8GeSe6 compounds, undergoing polymorphic transformations at 330 and 335 K, respectively. Based on solid-phase equilibria diagrams of the Cu-Ge-S(Se) systems, the potential-forming reactions responsible for the partial molar functions of copper in the alloys were determined and the thermodynamic functions of formation and standard entropies of both modifications of these compounds, as well as the thermodynamic functions of their polymorphic transitions, were calculated. The work also presents and analyzes the thermodynamic data for compounds of the argyrodite family available in the literature