INTERACTIONS IN THE QUASI-TERNARY SYSTEM Cu2S–Sb2S3–GeS2

Abstract

Phase equilibria between binary and ternary compounds that form at the respective boundary quasi-binary sections of the quasi-ternary system Cu2S–Sb2S3–GeS2 were invetigated. The study employed X-ray phase, microstructural and differential thermal analysis methods. Phase equilibria in the Cu2S–Sb2S3–GeS2 system at 500 K are represented by the isothermal section. The system is characterized by the interaction of phases with the formation of solid solution ranges α΄, β, γ, δ, ε of Cu2S, Sb2S3, Cu3SbS3, Cu8GeS6, Cu2GeS3, respectively, extending 5-10 mol. % at 570 K. The section features eight single-phase fields (solid solution ranges: α΄, β, γ, δ, ε of Cu2S, Sb2S3, Cu3SbS3, Cu8GeS6, Cu2GeS3, respectively, and compounds GeS2, Сu2GeS3, Cu4GeS4, and CuSbS2) that are separated by thirteen two-phase equilibria of which eight are at the bounding side systems (α΄ – γ, γ – CuSbS2, CuSbS2 – β, α΄ – δ, δ – Cu4GeS4, Cu4GeS4 – ε, ε – GeS2, and β – GeS2) and five inside the quasi-ternary system (γ – δ, γ – Cu4GeS4, γ – ε, CuSbS2 – ε, β – ε) that split the concentration triangle into 6 three-phase regions: α΄ – γ – δ, γ – δ – Cu4GeS4, γ – Cu4GeS4 – ε, CuSbS2 – γ – ε, β – CuSbS2 – ε, β – ε – GeS2. The existence of the CuSb5S8 compound was not confirmed. Phase diagrams of the Sb2S3–GeS2, Sb2S3–Cu2GeS3, and Cu3SbS3–Cu2GeS3 systems were investigated; these are of the eutectic type with the crystallization of solid solution ranges oh Sb2S3, Cu3SbS3, and Cu2GeS3. The coordinates of the eutectic point in the Sb2S3 – GeS2 system are 35 mol. % GeS2 at 747 K (L↔β+GeS2). The samples with 10-60 mol. % GeS2 content under these conditions are glass or ceramic-glass. The eutectic point in the Cu3SbS3 – Cu2GeS3 system lies at 7 mol. % Cu2GeS3 at 820 К (L↔γ΄+ε), with the peritectoid process at 760 К related to the polymorphous transition of Cu3SbS3 (γ΄+ε↔γ). The eutectic in the Sb2S3 – Cu2GeS3 system is at 18 mol.% Cu2GeS3 at 710 К (L↔ β+ε).