Flux dynamics, superconducting, and normal state properties of Gd(Ba $\mathsf{_{2-x}}$ Pr $\mathsf{_{x}}$ )Cu $\mathsf{_{3}}$ O $\mathsf{_{7 + \delta}}$

Gd(Ba 2-x Pr x )Cu 3 O $_{7 + \delta}$ single phase polycrystalline samples with $0.0\le x\le 1.0$ were investigated for structural, electronic and flux dynamics properties. Two-dimensional variable range hopping (VRH) is the dominant conduction mechanism in the normal state of the system. Pr doping strongly localizes the carriers in normal state, and finally causes the suppression of superconductivity. The effect of Pr substitution in 123 structure of HTSC at R or Ba sites is to increase the pseudogap temperature $T_{\rm s}$ , although, Pr at Ba sites has a stronger effect on the increase of $T_{\rm s}$ and suppression of superconductivity. The magnetoresistance of the samples have been studied within thermally activated flux creep and the Ambegaokar and Halperin phase slip models. The derived critical current density, H c2 (T), H c2 (0), and superconducting coherence length $\xi $ show that the Pr doping, like weak links, decreases the vortex flux pinning energy. Our results imply that understanding the real suppression mechanism of superconductivity by Pr doping in HTSC is connected crucially to the exact position of Pr in the structure. Copyright Springer-Verlag Berlin/Heidelberg 2004