Thermodynamic Properties of Iron-Gallium Sulfides

Results are presented from a thermodynamic study of compounds with a layered FeGa₂S₄ and Fe₂Ga₂S₅ structure. The EMF is measured for concentration chains of the type (−) FeS(solid)|glycerol + KCl + FeCl₂|(Fe in alloy) (+) in the 300–390 K range of temperatures. Results from X-ray diffraction analysis and data in the literature are used to establish the nature of solid-phase equilibria in the system Fe–Ga–S in the area of compositions FeS–Ga₂S₃–S. The formation of the above ternary compounds and a wide range of solid solutions based on Ga₂S₃ is confirmed. Partial molar functions of iron in ternary alloys are determined by combining thermodynamic data calculated from measurements of the EMF and the thermodynamic functions in the literature for compounds FeS₂ and FeS. These partial molar values and thermodynamic data for Ga₂S₃ are used to calculate the standard entropies and thermodynamic functions of the formation of compounds FeGa₂S₄ and Fe₂Ga₂S₅, and of solid solutions based on Ga₂S₃, according to the diagram of solid phase equilibria for subsystem FeS–Ga₂S₃–S.