THE CA SUBSTITUTION AND OXYGEN-CONTENT OF THE BI2SR2(CAXY1-X)CU2OY SYSTEM AND ITS STANDARD ENTHALPIES OF FORMATION

The enthalpy changes for the formation reaction, Delta H, of the super conducting related oxide Bi2Sr2(CaxY1-x)Cu2Oy system from the simple o xides, Bi2O3, SrO, CaO, Y2O3 and CuO, were determined by the solution calorimetric method using a perchloric acid solution containing 1x10(- 4) mol iron (II) perchlorate hexahydrate. The standard enthalpies of f ormation, Delta(f)H degrees, of the Bi2Sr2(CaxY1-x)Cu2Oy system were c alculated from the Delta H and Delta(f)H degrees values of the simple oxides. The enthalpy changes for the formation reaction in terms of mo le of atoms, Delta H-R, were calculated by dividing Delta H by upsilon , the number of atoms in a formula unit. On the basis of enthalpy, dis cussion was developed on the relation between the chemical stability o f the complex oxide, the superconducting region and structure change. The enthalpy change for the formatin reaction, \Delta H-R\, of the Bi2 Sr2(CaxY1-x)Cu2Oy system increased with increasing Ca substitution, x, and indicated a thermodynamic stability from the view point of enthal py. The heats of solution of each sample composition, which was anneal ed at various temperatures, and oxygen partial pressures and oxygen co ntents, were measured. The enthalpy changes for the formation reaction , \Delta H-R\, were increased with increasing oxygen content for each composition and indicated thermodynamic stability.