Two-dimensional mechanism of electrical conductivity in Gd_1−xCe_xBa₂Cu₃O_7−δ

Abstract

Partial substitutions of Pr and Ce are known to suppress the superconducting state in REBa 2 Cu 3 O 7−δ systems. We have substituted Ce for Gd in Gd 1−x Ce x Ba 2 Cu 3 O 7−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, T c decreases, the transition temperature width increases, and in the normal state a metal-insulator transition (MIT) occurs at x c = 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.

FLUCTUATION-INDUCED CONDUCTIVITY OF POLYCRYSTALLINE Er1-xTbxBa2Cu3O7-δ SUPERCONDUCTORS

“…Gd has a high magnetic moment and as the Pr concentration is increased in Gd 1−x Pr x Ba 2 Cu 3 O 7−δ compound, T C decreases monotonically, with superconducting state vanishing at a concentration of x = 0.45 [14]. For Gd 1−x Ce x Ba 2 Cu 3 O 7−δ , Mofakham et al observed in the normal state a metal-insulator transition for x ∼ = 0.12 and the disappearance of the superconducting state for x ∼ = 0.6 [15].…”