Phase Equilibria in the Ag2S–Sb2S3–SnS2 System and the Novel Quaternary Chalcogenide Ag11Sb3SnS12

Interactions of Ag and Sb(III) and Sn(IV) sulfides were investigated by x-ray diffraction, differential thermal analysis and microstructure analysis methods. The quaternary compound Ag₁₁Sb₃SnS₁₂ was found for the first time in the Ag₂S-Sb₂S₃-SnS₂ system at 500 K (227 °C) at the intersection of AgSbS₂-Ag₈SnS₆ and Ag₃SbS₃-Ag₂SnS₃. The compound melts congruently at 920 K (647 °C) and has a polymorphous transition at 646 K (373 °C). The quasi-ternary system is characterized by solid solution ranges of the binary compounds Ag₂S, Sb₂S₃, SnS₂, ternary Ag₃SbS₃, AgSbS₂, Ag₈SnS₆, Ag₂SnS₃ and quaternary compound Ag₁₁Sb₃SnS₁₂. The separation of the composition triangle into 10 single-phase, 18 two-phase, and 9 three-phase fields was established. Seven vertical sections were investigated of which five are quasi-binary (Ag₃SbS₃-Ag₈SnS₆, Ag₃SbS₃-Ag₂SnS₃, AgSbS₂-Ag₈SnS₆, AgSbS₂-Ag₂SnS₃, AgSbS₂-SnS₂). The AgSbS₂-Ag₄Sn₃S₈ and AgSbS₂-Sb₂SnS₅ sections are non-quasi-binary due to peritectic formation of Ag₄Sn₃S₈ and Sb₂SnS₅. The liquidus surface projection of the Ag₂S-Sb₂S₃-SnS₂ system consists of 10 fields of primary crystallization of the solid solutions α-Ag₂S, β-Sb₂S₃, γ-SnS₂, δ-Ag₃SbS₃, ε′-AgSbS₂, ζ-Ag₈SnS₆, η-Ag₂SnS₃, σ-Ag₁₁Sb₃SnS₁₂ and compounds Ag₄Sn₃S₈ and Sb₂SnS₅. These are separated by curves of monovariant equilibria that converge at 9 ternary invariant points (7 eutectic (E₁-E₇) and 2 quasi-peritectic (U₁, U₂)).