Phase equilibrium in Cu₂SnS₃-Cu₃SbS₃ system

It is known that triple thio- and selenostannates of copper and silver of the A₂SnX₃ type (A-Cu, Ag; X = S, Se), belonging to the class of diamond-like semiconductors, attract attention as promising functional materials for use in optical devices and photodiodes, such as converters of solar energy to electric. Therefore, the aim of this work is to study phase equilibrium and build a state diagram of the Cu2SnS3-Cu3SbS3 system. For research, the initial sulfides (Cu3SbS3 and Cu2SnS3) were synthesized from elements of high purity in quartz ampoules evacuated to 0.133 Pa. Quaternary alloys of the Cu2SnS3-Cu3SbS3 systems were synthesized from ligatures at a temperature of 900-1150 K, depending on the composition. To homogenize the alloys, annealing was performed at 50-60 K below solidus for 200 hours Using complex methods of physicochemical analysis (differential thermal, X-ray phase, microstructural, microhardness measurement and density determination), phase equilibria in the quasi-three-dimensional system Cu₂S-SnS₂-Sb₂S₃ were studied from sections of Cu₂SnS₃-Cu₃SbS₃. It is established that the Cu₂SnS₃-Cu₃SbS₃ system is a quasibinary section of the eutectic type and its state diagram is constructed. The coordinates of the eutectic correspond to 75 mol.% Cu₃SbS₃ and a temperature of 780 K. Based on the initial components in the section, the regions of solid solutions were determined. At room temperature, the regions of solid solutions based on Cu₂SnS₃ (9 mol % Cu₃SbS₃) and based on Cu₃SbS₃ (7 mol % Cu₂SnS₃) were revealed. At a eutectic temperature, solubility reaches 17 and 19 mol %, Respectively. Solid solutions based on ternary sulfide Cu2SnS3 crystallize in monoclinic syngony. With an increase in the content of Cu₃SbS₃, the monoclinic lattice parameters increase from a = 6.653, b = 11.537, c = 6.665 Å to a = 6.783, b = 11.727, c = 6.798 Å. These solid solutions are of the type of substitution. For structural and optical measurements, technological conditions for the growth of crystals of solid solutions were developed and their single crystals were grown. Single crystals of (Cu₂SnS₃) _1-x (Cu₃SbS₃) _x solid solutions were obtained by the Bridgman-Stockbarger method. The boundaries of α (Cu₂SnS₃) and β (Cu₃SbS₃) solid solutions were refined using the temperature-concentration dependence of the Gibbs free energy calculated using a modified version of the asymmetric model of regular solutions of nonmolecular compounds.

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