Abstract
The enthalpy changes for the formation reaction, ΔH, of the superconducting related oxide Bi2Sr2(CaxY1-x)Cu2Oy system from the simple oxides, Bi2O3, SrO, CaO, Y2O3 and CuO, were determined by the solution calorimetric method using a perchloric acid solution containing 1×10-4mol iron (II) perchlorate hexahydrate. The standard enthalpies of formation, ΔfH°, of the Bi2Sr2(CaxY1-x)Cu2Oy system were calculated from the ΔH and ΔfH° values of the simple oxides. The enthalpy changes for the formation reaction in terms of mole of atoms, ΔHR, were calculated by dividing ΔH by v, the number of atoms in a formula unit. On the basis of enthalpy, discussion was developed on the relation between the chemical stability of the complex oxide, the superconducting region and structure change. The enthalpy change for the formatin reaction, |ΔHR|, of the Bi2Sr2(CaxY1-x)Cu2Oy system increased with increasing Ca substitution, x, and indicated a thermodynamic stability from the view point of enthalpy. The heats of solution of each sample composition, which was annealed at various temperatures, and oxygen partial pressures and oxygen contents, were measured. The enthalpy changes for the formation reaction, |ΔHR|, were increased with increasing oxygen content for each composition and indicated thermodynamic stability.
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