HIGH-TEMPERATURE STABILITIES OF TERNARY OXIDES IN THE SM-CU-O SYSTEM

The determination of stability domains of the ternary oxides in the Ln -Cu-O oxides in the T-P-O2 space is gaining importance in the synthesi s of well-characterized materials for a wide variety of applications. For this purpose, oxygen potentials in the three phase system Sm2CuO4- Sm2O3-Cu2O was measured against air and Cu2O-CuO as reference electrod es over the temperature ranges 968-1203 K and 1017-1088 K respectively by using the oxide-electrolyte emf technique. These results led to th e least-squares expression Delta G(f,ox)degrees(Sm2CuO4) +/- 0.72(kJ m ol(-1)) = -16.05 + 0.0037T(K), where Delta G(f,ox)degrees(Sm2CuO4) sta nds for the standard Gibbs energy of formation of Sm2CuO4 from the con stituent binary oxides. Similarly, measurements on the cell Sm2CuO4-Sm CuO2-Sm2O3 yielded the expression Delta G(f,ox)degrees(SmCuO2) +/- 0.7 1(kJ mol(-1)) = -20.27 + 0.0067T(K). Another set of measurements on th e cell SmCuO2-Sm2O3-Cu when combined with Cu-Cu2O gave Delta G(f,ox)de grees(SmCuO2) +/- 0.59(kJ mol(-1)) = -32.47 + 0.0266T(K). The consiste ncy of the results on Delta G(f,ox)degrees of the two ternary oxides i s discussed in the light of possible non-stoichiometry in SmCuO2. The plots of log P-O2-1/T for the three phase mixtures with those for the standard copper oxide buffer mixtures are compared. (C) 1997 Elsevier Science B.V.