Gibbs energies of formation of cuprous and cupric yttrates (CuYO2 and Cu2Y2O5) and phase relations in the system copper-yttrium-oxygen
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Thermodynamic properties of cuprous and cupric yttrates (CuYO 2 and Cu 2 Y 2 O 5 ) 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 + CuYO 2 + Y 2 O 3 ||(Y 2 O 3 )ZrO 2 ||Cu + Cu 2 O, Pt; Pt, CuYO 2 + Cu 2 Y 2 O 5 ||(Y 2 O 3 )ZrO 2 ||Cu 2 O + CuO, Pt; and Pt, CuYO 2 + Cu 2 Y 2 O 5 + Y 2 O 3 ||(Y 2 O 3 )ZrO 2 ||Cu 2 O + CuO, Pt. Yttria-stabilized zirconia was used as the solid electrolyte in the temperature range 873-1323 K. The compound CuYO 2 was prepared by the reduction of Cu 2 Y 2 O 5 at 1373 K under argon gas with a residual oxygen partial pressure of ~Pa. For the reaction ½ Cu 2 O(s) + ½ Y 2 O 3 (s) → CuYO 2 (s), Δ G° = -5800 + 3.90T (± 30) J mol -1 , and for 2CuO(s) + Y 2 O 3 (s) → Cu 2 Y 2 O 5 (s), Δ G° = 11 210 - 15.072T (± 120) J mol -1 . The oxygen potentials corresponding to the coexistence of phases CuYO 2 + Cu 2 Y 2 O 5 and CuYO 2 + Cu 2 Y 2 O 5 + Y 2 O 3 were found to be the same over the temperature range of measurement, thus indicating negligible solid solubility of Y 2 O 3 in CuYO 2 and Cu 2 Y 2 O 5 . 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.