Structure and properties of phases in the Cu2-ХSe-Sb2Se3 system. The Cu2-XSe-Sb2Se3 phase diagram

•The Cu2−XSe-Sb2Se3 system phase diagram was revisited and reconstructed.•The samples of CuSbSe2 and Cu3SbSe3 annealed at 450 °C 4320 h are single-phase.•Cu3SbSe3 and CuSbSe2 melt incongruently, ΔН(Cu3SbSe3) = 67.6 J/g ΔН(CuSbSe2) = 85.1 J/g.•CuSb3Se5 is formed at 445 °C, ΔНf = 21.5 J/g, and decomposes at 527 °C, ΔНd = 36.7 J/g.•Thermal expansion anisotropy for CuSbSe2 and Sb2Se3 is similar to As2S3 and AsS. The phase diagram of the Cu2−XSe-Sb2Se3 system is revisited to clarify ambiguity/disagreement in previously reported data. Ternary Cu3SbSe3 and CuSbSe2 compounds were obtained. In order to confirm that the phases have been identified correctly, crystal structures were solved, and the energy band gaps measured. For the sample containing 75 mol% Sb2Se3 and 25 mol% Cu1.995Se the temperature range of the stability of the high-temperature CuSb3Se5 phase was determined for the first time. This phase is formed at 445 °С, decomposes following a peritectic reaction at 527 °С, and can be quenched. A high-temperature X-ray diffraction study of a sample containing 75 mol% Sb2Se3 and 25 mol% Cu2Se allowed us to measure the thermal expansion of the CuSbSe2 and Sb2Se3 phases present in the sample. The anisotropy of thermal expansion of CuSbSe2 is similar to that of As2S3 (orpiment); thermal expansion of Sb2Se3 is similar to that of AsS (realgar). The 6 balance equations of the invariant phase transformations involving all the ternary compounds existing in the Cu2−XSe-Sb2Se3 system were suggested for the first time. The temperature and the enthalpies of all these transformations were measured. A phase diagram of the Cu2−XSe-Sb2Se3 system was found for the first time in all the range of concentrations at temperatures from ambient to the complete melting. This diagram takes into consideration the phase equilibria that involve all the ternary compounds that are possible in this system. The liquidus of the Cu2−XSe-Sb2Se3 system was calculated according to Redlich-Kister equation; it agrees with the experimental data within 1–17 °С.