Experimental thermodynamic study of the equilibrium phase AgBi ₃S₅ by an improved EMF method

A thermodynamic study of the equilibrium phase assemblages AgBi ₃S₅-Bi₂S₃-S/Bi was made by an EMF-technique. The ternary phase was synthesized from the pure Ag₂S and Bi₂S₃ in an evacuated silica ampoule, and ground into powder before mixing with appropriate compositions of Bi₂S ₃ and S or Bi. The phase mixtures were pressed into different pellets, in a series of experiments. Together with pieces of pure Ag-foil and the electrolytic pellets of superionic conductor RbAg₄I₅ or AgI, the pellets were assembled to form the galvanic cells Pt(-) | Ag | RbAg₄I₅ | AgBi₃S₅ + Bi ₂S₃ + S + (C) | Pt(+) and Pt(-) | Ag | AgI | AgBi ₃S₅ + Bi₂S₃ + Bi | C | Pt(+). The EMF-measurements were made in a temperature range 299.15-594.15 K. In this paper, the thermodynamic functions for the formation of pavonite (AgBi ₃S₅) at sulfur and bismuth saturation have been determined. The obtained results are in agreement with some of the available literature values. Furthermore, new experimental thermodynamic data of bismuth-saturated pavonite (AgBi_3+xS₅; 0 < x < 0.14), in the temperature range 299.15-594.15 K, were determined.