Experimental thermodynamic study of the equilibrium phase AgBi3S5 by an improved EMF method

• A new method for constructing and measuring on galvanic cells has been employed.
• Galvanic cells including AgI and RbAg4I5 solid electrolytes were measured accurately.
• Thermodynamics of the phase assemblages AgBi3S5–Bi2S3–S/Bi have been investigated.
• ΔfG° values for sulfur- and bismuth-saturated pavonite (AgBi3S5) have been determined.
• New experimental thermodynamic data for bismuth-saturated pavonite were generated.

A thermodynamic study of the equilibrium phase assemblages AgBi3S5–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 Bi2S3 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 + Bi2S3 + S + (C) | Pt(+) and Pt(−) | Ag | AgI | AgBi3S5 + 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 (AgBi3S5) 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 (AgBi3+xS5; 0 < x < 0.14), in the temperature range 299.15–594.15 K, were determined.