Phase Equilibria in the Cu2S-La2S3-EuS System

Phase equilibria in the isothermal (970 K) and polythermal LaCuS2-EuS, Cu2S-EuLaCuS3, LaCuS2-EuLa2S4, and EuLaCuS3-EuLa2S4 sections of the Cu2S-La2S3-EuS system have been studied. EuLaCuS3 (annealing at 1170 K) is of orthorhombic system, space group Pnma, a = 8.1366(1)angstrom , b = 4.0586(1)angstrom , c = 15.9822(2)angstrom , is isostructural to Ba2MnS3, and incongruently melts by the reaction EuLaCuS3cryst (0.50 EuS; 0.50 LaCuS2) <-> 0.22 EuS SS (0.89 EuS; 0.11 LaCuS2) + 0.78 liq (0.39 EuS; 0.61 LaCuS2); Delta H = 52 J/g. The Cu2S-La(2)S3-EuS system has been found to contain five major subordinate triangles. At 970 K, tie-lines lie between EuLaCuS3 and the Cu2S, EuS, LaCuS2, and EuLa2S4 phases and between the LaCuS2 phase and the gamma-La2S3-EuLa2S4 solid solution. Eutectics are formed between LaCuS2 and EuLaCuS3 at 26.0 mol % of EuS and T = 1373 K and between EuLaCuS3 and EuLa2S4 at 29.0 mol % of EuLa2S4 and T = 1533 K.