Two-dimensional mechanism of electrical conductivity in Gd1-xCexBa2Cu3O7-δ

Partial substitutions of Pr and Ce are known to suppress the superconducting state in REBa2Cu3O7-δ systems. We have substituted Ce for Gd in Gd1-xCexBa2Cu3O7-δ compounds with x = 0.0-0.6 by the standard solid-state reaction technique. X-ray diffraction (XRD) experiments are performed and their results are refined by the Rietveld method. XRD analysis shows a predominantly single-phase perovskite structure with few impurity phases. Our resistivity results show that, by increasing the Ce content, Tc decreases, the transition temperature width increases, and in the normal state a metal-insulator transition (MIT) occurs at xc 0.12. The normal state resistivity of the samples and their slopes change at this point. The normal state resistivity of the samples is fitted with the variable range hopping (VRH) and the Coulomb gap (CG). Our results are most consistent with the two-dimensional VRH model