Low-temperature synthesis and phase equilibria in the Y-Cu-O binary system

The low-temperature phase relations in the Y-Cu-O system were examined using ultrasonically prepared, freeze-dried nitrate precursors. Under 1 atm of oxygen, Y2Cu2O5 was found to be stable above 955 ± 5 K; below this temperature, the component binary oxides CuO and Y2O3 are the only stable phases in the system. The entropy of formation of Y2Cu2O5, with respect to the component oxides, was calculated to be 5.3 ± 2.3 J/(mol·K) at 955 K. Bond valence analyses indicate that the entropy stabilization of this compound is most likely caused by the underbonded character of the copper ions