High-temperature equilibrium between YBa2Cu3-xCoxO6+delta solid solutions and oxygen

The equilibrium oxygen content of YBa2Cu3 - xCoxO6 + delta (0.2 less than o r equal to x less than or equal to 0.8) solid solutions was determined by c oulometric titration at temperatures in the range 600-850 degrees C and oxy gen pressures 1 less than or equal to p(O2) less than or equal to 10(5) Pa. The partial enthalpy and entropy of oxygen dissolution were evaluated as a function of composition, The thermodynamic functions were found to change sharply near the high- and low-oxygen limits of the solid solution, The res ults are interpreted in terms of a quasi-chemical model considering three i nequivalent oxygen sites in the basal plane.