Abstract
Bulk superconducting samples of type GdBa2Cu3-x Ru (x) O7-delta , Gd-123, with x=0.0-0.3 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD), scanning electron microscope (SEM), electron dispersive X-ray (EDX) and electrical-resistivity measurements were performed in order to investigate the effect of Ru4+ ions substitution on Gd-123 phase. Enhancement of both phase formation and the superconducting transition temperature T (c) for GdBa2Cu3-x Ru (x) O7-delta phase up to x=0.05 was observed from XRD and electrical-resistivity measurement, respectively. This enhancement was confirmed with the calculated relative volume fraction. For x > 0.05, suppression of both phase formation and T (c) was obtained and the superconductivity was completely destroyed around x=0.3. The normal-state electrical resistivity was analyzed by the two- and three-dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap CG. The results showed that the dominant mechanism was CG for xa parts per thousand currency sign0.075, while was 3D-VRH for xa parts per thousand yen0.15.