Phase equilibria in the BaS-Cu2S-Gd2S3 system

Phase equilibria in the BaS-Cu2S-Gd2S3 system have been studied along the 800 K isothermal section and the CuGdS2-BaS, Cu2S-BaGdCuS3, BaGdCuS3-Gd2S3, and BaGdCuS3-BaGd2S4 polythermal sections. Complex sulfide BaGdCuS3 is formed in the title system; it has an orthorhombic KZrCuSe3-type structure (space group Cmcm) with the unit cell parameters equal to a = 0.40529(2) nm, b = 1.34831(6) nm, c = 1.02940(5) nm. This sulfide melts congruently at 1685 K. BaGdCuS3 is in equilibrium with sulfides Cu2S, BaS, Gd2S3, CuGdS2, BaGd2S4, BaCu4S3, and BaCu2S2 and with compositions in the C0 solid-solution region of the Cu2S-Gd2S3 system. Eutectics are formed between compounds CuGdS2 and BaGdCuS3 at 7.0 mol % BaS and T = 1325 K, between BaGdCuS3 and BaS at 64.0 mol % BaS and T = 1625 K, between Cu2S and BaGdCuS3 at 8.0 mol % BaGdCuS3 and T = 1125 K, between Gd2S3 and BaGdCuS3 at 64.0 mol % Gd2S3 and 1495 K, and between BaGdCuS3 and BaGd2S4 at 35 mol % BaGd2S4 and T = 1660 K.