The role of Nb substitution in Cu 1− xTl xBa 2Ca 2− yNb yCu 3O 10− δ ( y = 0, 0.25, 0.5, 0.75, 1.0) superconductor

Abstract

The effects of higher electro-negativity Nb substitution at the Ca site in Cu 1− x Tl x Ba 2Ca 2− y Nb y Cu 3O 10− δ [Cu 1− x Tl x Nb y -1223] ( y = 0.25, 0.5, 0.75, 1.0) superconductor have been investigated. It is observed from these studies that lower doping concentration of Nb ( y = 0.25) improves the inter-plane coupling, however, coupling of CuO 2 planes is reduced with higher Nb doping. The higher concentration of Nb increases the density of oxygen in the charge reservoir layer and a material with over-doped carriers in CuO 2 planes is formed. The post-annealing in a N 2 atmosphere has been found to improve the superconducting properties of the final compound, however, O 2 annealing promotes the formation of material with inferior superconducting properties. The magnitude of diamagnetism is increased with post-annealing in a nitrogen atmosphere; as N 2 annealing helps in the formation of material with optimum carrier concentration in CuO 2 planes which is possibly done by the change in charge state of thallium from Tl 3+ to Tl 1+.