Preparation of Alloys and Investigation of Phase Equilibria in the CuFeS2-δ-CuGaS2 System

Alloys of the CuFeS2-delta-CuGaS2 system were synthesized by solid-state chemical reactions from the corresponding mixtures of powders of the CuFeS2-delta and CuGaS2 ternary compounds. Phase equilibria were investigated using x-ray powder diffraction (XRPD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) combined with energy-dispersive x-ray spectroscopy (EDX). It was found that the T-x phase diagram of the (CuFeS2-delta)(1-x)-(CuGaS2)(x) system has a peritectic character with no solubility at room temperature in the composition range x = 0.34-0.94. The lack of complete solubility can be explained by the fact that the crystal structures of the starting ternary compounds CuFeS2-delta and CuGaS2 are different. Samples of the homogeneous chalcopyrite, having the chemical composition of CuFeS2-delta, possess deficiency of sulfur and exist in the defect chalcopyrite structure at room temperature, but the region of existence of the CuGaS2 compound includes the stoichiometric composition, and the samples crystallize in the ideal crystal structure of chalcopyrite.