Relative thermodynamic stabilities of constituent oxides of high Tc superconductors

A thermodynamic scale of the relative stabilities of constituent oxides can help the choice of stoichiometric multi-component compositions and can provide guidance for judicious selection of heat-treatment conditions for high-Tc superconductors. A thermodynamic analysis was undertaken to study Y2O3-BaO-CuO, BaO-K2O-Bi2O3 and La2O3-SrO-NiO systems. The relative stability of the oxides was expressed in terms of two ratios, Sv and Sp computed using free-energy of formation and vapour pressure data. CuO, Bi2O3 and NiO were taken as reference oxides for YBa2Cu3Osub(7-δ), Basub(0.6)Ksub(0.4)BiO3 and Lasub(1.9)Srsub(0.1)NiO4 respectively. Thermodynamically, the reference oxide was found to be the least stable amongst the constituent oxides in each of these systems. (author). 8 refs., 4 figs