Gibbs Energies of Formation of CuYO2 and Cu2Y2O5 and Phase Relations in the System Cu-Y-O

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 parallel to(Y2O3)ZrO2 parallel to Cu + Cu2O, Pt; Pt, CuYO2 + Cu2Y2O5||(Y2O3)ZrO2|parallel to Cu2O + CuO, Pt; and Pt, CuYO2 + Cu2Y2O5 + Y2O3 parallel to(Y2O3)ZrO2 parallel to 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 similar to 1 Pa. For the reaction 1/2Cu(2)O(s) + 1/2Y2O(3)(s) -> CuYO2(s), Delta G degrees = -5800 + 3.90T (+/- 30) J mol(-1), and for 2CuO(s) + Y2O3(s) -> Cu2Y2O5(s), Delta G degrees = 11210 - 15.07T (+/- 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-O system at 723, 950, and 1373 K have been deduced.