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

The granular Gd1-x-zPrxCazBa2Cu3O7-δ (GdPrCa-123) high-temperature cuprate superconductor samples were prepared and characterized. The electrical resistivity of Pr-free samples show a reduction in Tc with increasing Ca content. For these samples, the Tc(z) curve is nonlinear and a plateau appears at z approx. 0.05-0.15. With increasing Ca concentration, the lattice 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 hand, the Cu(2)-O(2)-Cu(2) angle increases and the CuO2 plane becomes flatter with successive Ca doping, which causes the suppression of superconductivity. The same bond distances in Pr-Ca substituted samples decrease slowly with increasing Ca doping, but increase with increasing Ca concentration after an optimum value. In addition, the electrical resistivity of Pr-Ca-doped samples shows an increase of Tc with Ca doping up to an optimum value, whereafter it begins to decrease. We suggest that the competition of two effects, the number of holes and the flattening of CuO2 planes by Ca doping, results in a nonlinear decrement in the Tc(z) curve. (author)