THERMOGRAVIMETRIC AND STRUCTURAL INVESTIGATIONS OF PRXY1-XBA2CU3O7-DELTA

In a series of samples of the composition PrxY1-xBa2Cu3O7-δ an orthorhombic structure was found in the full concentration range 0≤x≤1. The difference of the lattice parameters, b-a, remains constant with increasing x. The oxygen content of samples sintered under the same conditions is not influenced by the praseodymium content. The phase transition from an orthorhombic to a tetragonal structure, which takes place during heating of the samples, was investigated by thermogravimetry. Using samples which had been pretreated under reducing conditions plateaus appear in the thermograms. The effect can be observed during both the heating period and in a subsequent cooling down. With increasing praseodymium content the temperature at which the oxygen reaction starts decreases for reduction as well as for oxidation of samples that had been reduced prior to treatment. The amounts of the changes of the entropy and of the enthalpy for the formation of oxygen defects in the orthorhombic phase decrease with increasing Pr-content, but they remain constant in the tetragonal phase at least for x<0.5. © 1990.