Phase Equilibria in Systems DyCuS2–EuS and Cu2S−Dy2S3−EuS

Abstract

The phase diagram of system DyCuS₂–EuS has been first constructed, and the phase equilibria in the Cu₂S–Dy₂S₃–EuS triangle at 970 K have been studied. Compound EuDyCuS₃ (1DyCuS₂ : 1EuS), space group Pnma, a = 10.1901(3) Å, b = 3.9270(1) Å, c = 12.8468(3) Å, melts incongruently at 1727 ± 7 K according to the reaction: EuDyCuS_3solid ↔ 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS₂) + 0.83 liq (42 mol % EuS, 58 mol % DyCuS₂), ΔH = 2.9 ± 0.6 kJ/mol; microhardness of the phase is 3080 ± 35 MPa. Compound EuDyCuS₃ is transparent in the range 3000–1800 cm^–1. In system DyCuS₂–EuS, the solid solution (SS) based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS₂, 2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS₂ and EuDyCuS3 at 12 mol % EuS, T = 1487 ± 8 K. In system Cu₂S−Dy₂S₃−EuS, 10 secondary systems have been isolated. At 970 K, tie-lines are located between compound EuDyCuS₃ and solid solutions based on compounds β-Cu₂S, EuS, DyCuS₂, β-(DyCu₃S₃), and EuDy₂S₄; between DyCuS₂ and the solid solution of α-Dy₂S₃, DyCuS₂, and EuDy₂S₄.