PHASE EQUILIBRIA IN THE SYSTEMS Cu(Ag)2S – Sb2S3 – SnS2

Abstract

Phase equilibria in the quasi-ternary systems Cu(Ag)2S – Sb2S3 – SnS2 were investigated by X-ray diffraction, differential thermal and microstructure analysis methods. Isothermal sections at 500 K and key vertical sections of these systems were plotted from obtained results. It was established that the copper-containing system at the annealing temperature features six two-phase equilibria between binary and ternary compounds of the boundary side systems, with solid solutions upto 5-10 mol. %. Three vertical sections, Cu3SbS3 – Cu2SnS3, CuSbS2 – Cu2SnS3, Sb2S3 – Cu2SnS3, are quasi-binary systems of the eutectic type, with the coordinates 20, 7, and 13 mol. % Cu2SnS3 at 866 K, 796 K, 765 K, respectively. Two other sections, Sb2S3 – Cu4Sn7S16, Cu3SbS3 – Cu4SnS4, are non-quasibinary since Cu4Sn7S16 and Cu4SnS4 are formed in the solid phase, and Sb2SnS5 melts incongruently. The existence of a new quaternary compound of the Ag11SnSb3S12 composition was established for the first time in the Ag2S – Sb2S3 – SnS2 system at 500 K at the crossing of AgSbS2 – Ag8SnS6 and Ag3SbS3 – Ag2SnS3 sections. Nine twophase equilibria between ten compounds were found in the system, with the solid solubility of 5-15 mol. % along the sections. Five of seven vertical sections are quasi-binary systems (Ag3SbS3 – Ag8SnS6, Ag3SbS3 – Ag2SnS3, AgSbS2 – Ag8SnS6, AgSbS2 – Ag2SnS3, AgSbS2 – SnS2); the AgSbS2 – Ag4Sn3S8 and AgSbS2 – Sb2SnS5 sections are non-quasibinary due to peritectic formation of Ag4Sn3S8 and Sb2SnS5. The presented phase diagrams of the silver-containing sections Ag3SbS3 – Ag8SnS6, AgSbS2 – Ag8SnS6, AgSbS2 – Ag2SnS3 and AgSbS2 – SnS2 are of the eutectic type with coordinates 10 mol. % Ag8SnS6 at 738 K, 12 and 30 mol. % Ag8SnS6 at 747 K and 742 K, 30 mol. % Ag2SnS3 at 750 K, and 25 mol. % SnS2 at 741 K, respectively. The quaternary compound Ag11SnSb3S12 melts congruently at 920 K and has a polymorphous transitionat 649 K. The phase has variable composition, its homogeneity range extends from 16 to 27 mol. % Ag8SnS6 at the temperatures of invariant eutectic processes,and from 20 to 25 mol. % Ag8SnS6 at 500 K. The in variant processes associated with phase transitions of Cu3SbS3, AgSbS2 and Ag11SnSb3S12 have eutectoid character.