Nb Substituted Cu0.5Tl0.5Ba2(Ca3Nb1)Cu5O_{14-delta} and Cu0.5Tl0.5Ba2(Ca4Nb1)Cu6O_{16-delta} Superconductors

The effects of higher electro-negativity Nb substitution on the Ca site in Cu_0.5Tl_0.5Ba₂ (Ca₃Nb₁)Cu₅O $_{14-delta}$ and Cu_0.5Tl_0.5Ba₂(Ca₄Nb₁)Cu₆O $_{16-delta}$ superconductors have been investigated. The Nb doping has been found to increase the oxygen contents in Cu_0.5Tl_0.5Ba₂O $_{16-delta}$ 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 Cu_0.5Tl_0.5Ba₂Can _?2Nb₁Cun ₂ n+4?δ (n=5,6) with enhanced T _c's.