REVIVAL OF SUPERCONDUCTIVITY IN Y0.4PR0.6BA2CU3O7-DELTA BY THE ISOVALENT SUBSTITUTION OF SR

Polycrystalline samples of Y0.4Pr0.6Ba2-xSrxCu3O7-delta have been prep ared and characterized by x-ray powder diffraction, differential therm al analysis, and temperature dependence of resistivity and AC suscepti bility. We observed that both superconductivity and metallic conductiv ity were revived at x greater than or equal to 0.75, accompanied by an orthorhombic-to-tetragonal transition. The superconducting transition temperature could be further enhanced by increasing the Sr content, s uggesting that there is an ion-size effect on T-c at the Ba site. The results were discussed in terms of the Pr-O covalent bonding effect.