Temperature dependence of tellurium fugacity for the kotulskite (PdTe)–merenskyite (PdTe<inf>2</inf>) equilibrium determined by the method of a solid-state galvanic cell

The thermodynamic properties of the kotulskite (PdTe)/merenskyite (PdTe2) equilibrium in the Ag-Pd-Te system were determined for the first time by the electromotive force (EMF) method. The thermodynamic properties were calculated from the temperature dependence of the EMF in a completely solid-state electrochemical cell with a common gas space:(-) C (graphite)| Ag | RbAg 4I 5| Ag 2Te , PdTe , PdTe 2| C (graphite)(+) , following a virtual chemical reaction: 2Ag + PdTe 2↔ Ag 2Te + PdTe. The measurements were carried out in the temperature range of 371–488 K at the atmospheric pressure of pure argon. As a result, the thermodynamic properties for the reaction PdTe + Te = PdTe2 at a pressure of 1 bar (105 Pa) were determined as: ΔrGo/J·mol−1 = − 27,639; ΔrS/J mol−1 K−1 = − 21.98; ΔrHo/J·mol−1 = − 34,176. Fugacity of gaseous tellurium (Te2) over the PdTe + 1/2Te2 ↔ PdTe2 equilibrium was also calculated: log f Te2 = (9.205 ± 0.072) − (11.44 ± 0.03)·(1000/T), (371.7 < T/K < 493.6)