Nb Substitution Effects on Superconducting Properties ofRu1−xNbxSr2Eu1.4Ce0.6Cu2O10−δ

Abstract

In order to gain further insight into the role of substitution of Ru by Nb on superconductivity, polycrystalline samples of Ru1−xNbxSr2Eu1.4Ce0.6Cu2O10−δ  (0.0 ≤x≤ 1.0) have been synthesized by solid-state reaction method. Substitution of Nb at the Ru site in the system takes place isostructurally in the tetragonal structure (space groupI4/mmm) with full solubility (x= 1.0). Superconductivity exists for all compositions. Resistivity measurements in function of temperature from 0 to 300 K were done using the four-probe technique. It is found that the substitution of Ru5+for Nb5+depresses the superconductivity of samples fromTc = 29 K forx= 0.0 toTc = 5 K forx= 1.0 (whereTcis the critical temperature, when resistivity becomes equal to zero). In the normal state, the dependence of resistivity with temperature, for compositions withx = 0.0 and 0.2, shows a metallic behavior, while for compositions betweenx= 0.4 andx= 1 it shows a semiconducting behavior. In that way, the density of charge carriers is reduced with niobium doping, leading to the semiconducting behavior. The resistive transition to the superconducting state of all samples is found to be affected by granularity. Samples undergo double superconducting transition.