Thermodynamic properties of saturated solid solutions of Ag₇SnSe₅Br and Ag₈SnSe₆ compounds in the Ag–Sn–Se–Br system measured by the EMF method

Highlights: • Triangulation in the vicinity of Ag₇SnSe₅Br and Ag₈SnSe₆ compounds were established. • The equations of potential-forming process in electrochemical cells were determined. • The temperature dependences EMF cells have been defined. • The values of thermodynamic functions of compounds were calculated. • The influence Br⁻ on the symmetry of phases was analyzed. - Abstract: Triangulation of the Ag–Sn–Se–Br system in the part of Ag₂Se–SnSe–SnSe₂–AgBr was carried out using the X-ray diffraction and differential thermal analysis methods. The spatial position of the established four-phase regions regarding figurative point of silver was used in order to write the equations of virtual potential-forming chemical reactions. Potential-forming processes were performed in electrochemical cells (ECCs) of the type (−) C |Ag| Ag₃GeS₃Br glass |D| C (+) where C are the inert (graphite) electrodes; Ag and D are the electrodes of the ECCs; D represents the equilibrium four-phase alloys, and Ag₃GeS₃Br glass is a membrane with purely ionic Ag⁺ conductivity. The linear dependencies of the EMF of cells on temperature in the range of 480–520 Рљ have been used in order to calculate the standard thermodynamic values of saturated solid solutions of Ag₇SnSe₅Br and Ag₈SnSe₆ compounds in the four-element part of the Ag–Sn–Se–Br system.