Thermodynamic properties of Ag3AuSe2 from 300 to 500 K by a solid state galvanic cell

•Experimental thermodynamics data on Ag3AuSe2 compounds are obtained to 500 K.•A new phase transformation of Ag3AuSe2 at low temperature is proposed.•Advanced measurement makes possible to distinguish the phase transformation.

The numerical values of the standard thermodynamic functions of Ag3AuSe2 (fischesserite) in the Ag–Au–Se system were determined by the electromotive force (EMF) method in a solid state galvanic cell with RbAg4I5 as the solid electrolyte below 500 K. Ag3AuSe2 was synthesized from pure elements in stoichiometric composition by evacuated ampoules made of quartz glass. On the basis of EMF vs. temperature experimental data, the analytical equations were obtained, from which the temperature dependent relationships of the Gibbs energy in the relevant reactions and the standard thermodynamic functions of Ag3AuSe2 within the temperature range of 300–500 K were calculated. The results show that there is possible a new polymorphic transformation around 350 K.