Study of the 2Cu2S + GeSe2 ↔ 2Cu2Se + GeS2 reciprocal system and thermodynamic properties of the Cu8GeS6−xSex solid solutions

The phase equilibria in the 2Cu2S + GeSe2 ↔ 2Cu2Se + GeS2 reciprocal system were experimentally investigated by means of differential thermal analysis (DTA) and powder X-ray diffraction (PXRD) technique as well as electromotive force measurements (EMF) of concentration chains with Cu4RbCl3I2 solid electrolyte. Five isopleth sections Cu8GeS6-Cu8GeSe6, Cu8GeSe6-Cu2Se, Cu2GeS3-Cu8GeSe6, Cu2S-GeSe2 and Cu2Se-GeS2 and four isothermal sections at 300, 800, 1100 and 1200 K as well as liquidus surface projection of the system were constructed based on the experimental data. The system was found to be mutually reciprocal with the formation of continuous or wide areas of solid solutions series along the Cu2S-Cu2Se, Cu2GeS3-Cu2GeSе3, Cu8GeS6-Cu8GeSe6 and GeS2-GeSe2 binary systems. The partial molar thermodynamic functions of the copper for the Cu8GeS6-xSex (where x = 0.6; 1.2; 1.8; 2.4; 3.6; 4.8; 5.4 and 5.7) solid solutions were calculated based on the EMF measurements data.