Phase equilibria in the systems SrS-Cu2S-Ln2S3 (Ln = La or Nd)

Abstract

Phase equilibria in the systems SrS-Cu2S-Ln2S3 (Ln = La or Nd) have been studied along the isothermal section at 1050 K and vertical sections CuLnS2-SrS and Cu2S-SrLnCuS3, which are partially quasibinary joins. Compounds SrLnCuS3 with Ln = La or Nd have been synthesized for the first time. They crystallize in orthorhombic space group Pnma, the BaLaCuS3 structure type, with the following unit cell parameters: for SrLaCuS3, a = 1.1157(2) nm, b = 0.41003(6) nm, c = 1.1545(2) nm; for SrNdCuS3, a = 1.1083(1) nm, b = 0.40887(7) nm, c = 1.1477(2) nm. Noticeable homogeneity regions for SrLnCuS3 are not found. The compounds melt congruently by the reaction SrLnCuS3 ↔ SrS + L at 1365 K for SrLaCuS3 and 1400 K for SrNdCuS3. The tie-lines at 1050 K in the systems SrS-Cu2S-Ln2S3 radiate from SrLnCuS3 toward phases SrS, Cu2S, CuLnS2, and SrLn2S4, lying between the phases CuLnS2 and compositions from the γ-Ln2S3-SrLn2S4 solid-solution field. Eutectics are formed between the compounds CuLaS2 and SrLaCuS3 at 21.0 mol % SrS, T = 1345 K; between the compounds CuNdS2 and SrNdCuS3 at 31.0 mol % SrS, T = 1310 K; and between the phases Cu2S and SrLnCuS3 at 14.0 mol % SrLaCuS3, T = 1075 K and 8.0 mol % SrNdCuS3, T = 1055 K.