Phase Equilibria in Ag8SnS6 – Cu2SnS3 and Ag2SnS3 – Cu2Sn4S9 Systems

Abstract

Purpose. Chalcostannates of copper and silver are among the important functional materials of modern technology. Among them, there are materials with valuable semiconductor, photosensitive, and thermoelectric properties. By complex methods of physical-chemical analysis (differential thermal, X-ray phase, microstructural analysis, microhardness measurement, and density determination) phase equilibria have been studied in systems Ag8SnS6–Cu2SnS3 and Ag2SnS3–Cu2Sn4S9 and their T–x phase diagrams have been constructed. Results. It was shown that the Ag8SnS6–Cu2SnS3 system is a quasi-binary cross-section of the Ag2S–SnS2–Cu2S quasi-triple system and belongs to the simple eutectic type with limited solubility regions based on the initial sulphides. The coordinates of the eutectic point are: 50 mol % Ag2SnS3 and T = 900 K. The solubility based on Ag8SnS6 and Cu2SnS3 at the eutectic temperature stretches to 20 and 28 mol %, respectively. With decreasing temperature, the solid solutions decompose, and at 300 K they have values of 5 and 10 mol %. The phase transition a-Ag8SnS6 ↔ b-Ag8SnS6 occurs at 410 K and has a eutectoid character. It was established that with an increase in the concentration of Ag8SnS6 in solid solutions (Cu2SnS3)1–х (Ag8SnS6)х, the cubic lattice parameter increases from a = 0.5445 nm (for pure Cu2SnS3) to a = 0.725 nm (for composition x = 0.1). The concentration dependence of the lattice parameter on the composition is linear. Conclusion. The Ag2SnS3–Cu2Sn4S9 system, due to the peritectic melting of Cu2Sn4S9, has a complex character and is a partial quasi-binary section. The quasi-binary state is violated in the range of 65–100 mol % Cu2Sn4S9 and above temperature 900 K. The part of the system in the concentration range of 0–65 mol % Cu2Sn4S9, is of a eutectic type. Solid solutions based on Ag2SnS3 – Cu2Sn4S9 are narrow and at 300 K they are 10; 2.5 mol %, respectively.

Keywords

• system
• quasi-binary
• solid solution
• x-ray phase analysis
• structure
• eutectic.