The role of Nb substitution in Cu1−xTlxBa2Ca2−yNbyCu3O10−δ (y = 0, 0.25, 0.5, 0.75, 1.0) superconductor

The effects of higher electro-negativity Nb substitution at the Ca site in Cu1−xTlxBa2Ca2−yNbyCu3O10−δ[Cu1−xTlxNby-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 CuO2 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 CuO2 planes is formed. The post-annealing in a N2 atmosphere has been found to improve the superconducting properties of the final compound, however, O2 annealing promotes the formation of material with inferior superconducting properties. The magnitude of diamagnetism is increased with post-annealing in a nitrogen atmosphere; as N2 annealing helps in the formation of material with optimum carrier concentration in CuO2 planes which is possibly done by the change in charge state of thallium from Tl3+ to Tl1+.