Compounds of the argyrodite family and the phases based on them are of interest as environmentally friendly functional materials. This work presents new data on phase equilibria in the CuGeSe – AgGeS system obtained by differential thermal analysis and X- ray powder diffraction studies. It was established that the system is not quasi- binary due to the incongruent melting of CuGeSe yet it maintains thermodynamic stability below the solidus temperature. A continuous series of solid solutions (δ- phase) with both cationic and anionic substitutions was identified between the high- temperature modifications. Limited homogeneity regions were determined based on the low- temperature modifications. The formation of solid solutions lowers the temperatures of polymorphic transitions and expands the homogeneity range of the ion- conducting cubic δ- phase down to room temperature and below. At room temperature, the homogeneity range of the δ- phase spans 10- 70 mol. % AgGeS. The δ- phase within the composition range of 36- 64 mol. % AgGeS can be classified as a high- entropy alloy, which opens additional prospects for tailoring its properties through entropy- driven structural stabilization.
A.N. Poladova (2025) studied this question.