Phase equilibria in the Ag2Se–GeSe2–SnSe2 system and thermodynamic properties of Ag8Ge1–xSnxSe6 solid solutions

Abstract

The Ag₂Se–GeSe₂–SnSe₂ system has been studied in the temperature range 290–430 K using differential thermal analysis, X-ray diffraction, and emf measurements concerning silver concentration cells with Ag₄RbI₅ as a solid electrolyte. We have constructed a number of vertical sections; the 300-, 800-, and 900-K isothermal sections of the phase diagram; and a projections of the liquidus surface. It has been shown that the only pseudobinary join, Ag₈GeSe₆–Ag₈SnSe₆, contains a continuous series of solid solutions between the two crystalline phases of the constituent selenides and divides the system into two independent subsystems. Ag₂Se–Ag₈GeSe₆–Ag₈SnSe₆ is a univariant, eutectic subsystem, and GeSe₂–Ag₈GeSe₆–Ag₈SnSe₆–SnSe₂ is an invariant eutectic subsystem. Experimental emf data were used to evaluate partial thermodynamic functions of the silver in the high-temperature and low-temperature Ag₈Ge_1–xSn_xSe₆ solid solutions.