Nb Substituted Cu0.5Tl0.5Ba2(Ca3Nb1)Cu5O$$_{14-\delta}$$ and Cu0.5Tl0.5Ba2(Ca4Nb1)Cu6O$$_{16-\delta}$$ Superconductors

Abstract

The effects of higher electro-negativity Nb substitution on the Ca site in Cu0.5Tl0.5Ba2 (Ca3Nb1)Cu5O\(_{14-\delta}\) and Cu0.5Tl0.5Ba2(Ca4Nb1)Cu6O\(_{16-\delta}\) superconductors have been investigated. The Nb doping has been found to increase the oxygen contents in Cu0.5Tl0.5Ba2O\(_{16-\delta}\) charge reservoir layer of the final compound. The post-annealing in the N2 atmosphere has been found to improve the superconducting properties; however, O2 annealing produced the material with inferior superconducting properties. The quantity of diamagnetism is increased with post-annealing in the nitrogen atmosphere; as N2 annealing helps in the formation of material with optimum carriers concentration in the CuO2 planes, which is done by the change in the charge state of thallium from Tl3+ to Tl1+. The Nb substitution has been found to develop the higher CuO2 planner phases such as Cu0.5Tl0.5Ba2Can −2Nb1Cun 2 n+4−δ (n=5,6) with enhanced T c's.