Investigation of structure and transport properties of Gd1-x-zPrxCazBa2Cu3O7-delta system

The granular Cd1-x-zPrxCazBa2Cu3O7-delta (GdPrCa-123) high-temperature cupr ate superconductor samples were prepared and characterized. The electrical resistivity of Pr-free samples show a reduction in T-c with increasing Ca c ontent. For these samples, the T-c(z) curve is nonlinear and a plateau appe ars at z approximate to 0.05-0.15. With increasing Ca concentration, the la ttice parameter a increases. Moreover, it is observed that the in-plane Cu( 2)-O(2) bond distance increases with increasing Ca content. On the other ha nd, the Cu(2)-O(2)-Cu(2) angle increases and the CuO2 plane becomes flatter with successive Ca doping, which causes the suppression of superconductivi ty. The same bond distances in Pr-Ca substituted samples decrease slowly wi th increasing Ca doping, but increase with increasing Ca concentration afte r an optimum value. In addition, the electrical resistivity of Pr-Ca-doped samples shows an increase of T-c with Ca doping up to an optimum value, whe reafter it begins to decrease. We suggest that the competition of two effec ts, the number of holes and the flattening of CuO2 planes by Ca doping, res ults in a nonlinear decrement in the T-c(z) curve.