Gibbs energies of formation of cuprous and cupric yttrates (CuYO₂ and Cu₂Y₂O₅) and phase relations in the system copper-yttrium-oxygen

Abstract

Thermodynamic properties of cuprous and cupric yttrates (CuYO₂ and Cu₂Y₂O₅) and oxygen potentials corresponding to three three-phase fields in the system Cu-Y-O have been determined by using solid-state galvanic cells; Pt, Cu + CuYO₂ + Y₂O₃ ||(Y₂O₃)ZrO₂||Cu + Cu₂O, Pt; Pt, CuYO₂ + Cu₂Y₂O₅||(Y₂O₃)ZrO₂ ||Cu₂O + CuO, Pt; and Pt, CuYO₂ + Cu₂Y₂O₅ + Y₂O₃||(Y₂O₃)ZrO₂||Cu₂O + CuO, Pt. Yttria-stabilized zirconia was used as the solid electrolyte in the temperature range 873-1323 K. The compound CuYO₂ was prepared by the reduction of Cu₂Y₂O₅ at 1373 K under argon gas with a residual oxygen partial pressure of ~Pa. For the reaction ½ Cu₂O(s) + ½ Y₂O₃(s) → CuYO₂(s), Δ G° = -5800 + 3.90T (± 30) J mol^-1, and for 2CuO(s) + Y₂O₃(s) → Cu₂Y₂O₅(s), Δ G° = 11 210 - 15.072T (± 120) J mol^-1. The oxygen potentials corresponding to the coexistence of phases CuYO₂ + Cu₂Y₂O₅ and CuYO₂ + Cu₂Y₂O₅ + Y₂O₃ were found to be the same over the temperature range of measurement, thus indicating negligible solid solubility of Y₂O₃ in CuYO₂ and Cu₂Y₂O₅. On the basis of the present results and auxiliary thermodynamic data from the literature, phase relations in the Cu-Y-0 system at 723, 950, and 1373 K have been deduced.