Pr at Gd or Ba site in GdBa2Cu3O7:: Appearance of superconductivity -: art. no. 104516

Gd(Ba2-xPrx)Cu3O7+delta single phase polycrystalline samples with 0.0less than or equal toxless than or equal to1.0 were investigated for their structural and electronic properties. Due to the solubility limit, the 123 structure forms in the 0.0less than or equal toxless than or equal to0.50 range; for xgreater than or equal to0.6, a decomposition of the perovskite-type phases occurs. For x=0.2, there is an orthorhombic-tetragonal phase transition, concurrent with a metal-insulator transition, which is evident in the normal state resistivity. For x(c)=0.35, the superconductor-insulator transition occurs. An unusual hump has been observed on the resistivity vs temperature curve of the samples for particular values of Pr doping. Based on the Rietveld refinement of the x-ray diffraction patterns, and bond valence sum calculations, we have found that the Ba atom substitution at the rare earth site could lead to superconductivity in some parts of the grains at T(m)similar to80-90 K, which appears as a hump on the rho(T) curve. Our result is in line with the previously proposed possibility of the existence of superconductivity in Pr-123 due to the Ba atom substituted at the Pr site. We have also concluded that with increasing Pr doping, O(4) atoms migrate from their sites, and the O(5) occupation increases. So, perovskite substructures with Pr at the rare earth or Ba site, become identical. Hence, Pr at the Ba or rare earth site suppresses the superconductivity by the same mechanism(s).