Phase Equilibria in the Ag₂Se–Cu₂SnSe₃ and Ag₈SnSe₆–Cu₂SnSe₃ Systems

Abstract

The phase formation in the sections Ag₂Se–Cu₂SnSe₃ and Ag₈SnSe₆–Cu₂SnSe₃ of the quasi-ternary system Ag₂Se–SnSe₂–Cu₂Sе was studied for the first time by differential thermal analysis (with thermodynamic calculations), X-ray powder diffraction analysis, and microstructural analysis and also by microhardness and density measurements. No new quaternary compounds were detected. It was determined that both sections are quasi-binary and are of simple eutectic type with limited solubility based on the initial selenides. The coordinates of the eutectic points are (40 mol % Ag₂Se, 910 K) and (50 mol % Ag₈SnSe₆, 780 K). The solubility based on Cu₂SnSe₃ was 10 mol % Ag₂Se in the system Ag₂Se–Cu₂SnSe₃ and 15 mol % Ag₈SnSe₆ in the system Ag₈SnSe₆–Cu₂SnSe₃. Single crystals of the compound Cu₂SnSe₃ and the solid solutions (Cu₂SnSe₃)_{1 – х}(Ag₈SnSe₆)_х (х = 0.02–0.15) were grown by the Bridgman–Stockbarger directional crystallization method. It was found that these solutions crystallize in the monoclinic system, and the unit cell parameters increase with increasing Ag₈SnSe₆ content: а = 6.968–6.985 Å, b = 12.051–12.078 Å, с = 6.945–6.968 Å, β = 109.20°–109.30°, space group Сс, Z = 4, and ρ = 5.75–5.86 g/cm³.