STANDARD GIBBS FREE-ENERGY OF FORMATION OF BACUO2 AND BACU2O2 FROM OXIDES

Phase relations in the Cu-CuO-BaO system were studied by the equilibrium and quenching technique. In the temperature range 800-950-degrees-C three cuprates, i.e. BaCuO2, Ba2CuO3 and BaCu2O2, are stable in the system. The thermodynamic stabilities of BaCuO2, and BaCu2O2 were determined by means of the e.m.f. measurements for the following equilibria: BaCu2O2(s) = BaO(s) + 2Cu(s) + (1/2)O2(g) and 2BaCuO2(s) + Cu2O(s) = 2BaCu2O2(s) + (1/2)O2(g). From the data obtained on these three-phase combinations the following relationships were calculated for the Gibbs free energy: BaO(s) + Cu2O(s) = BaCu2O2(s) with DELTA-G(f)0 = -30358 + 0.90T (J mol-1); and BaO(s) + CuO(s) = BaCuO2(S) with DELTA-G(f)0 = -42900 + 7.8T (J mol-1).