Nb substituted Cu _0.5Tl _0.5Ba ₂(Ca ₃Nb ₁)Cu ₅O _14-δ and Cu _0.5Tl _0.5Ba ₂(Ca ₄Nb ₁)Cu ₆O _16-δ Superconductors

The effects of higher electro-negativity Nb substitution on the Ca site in Cu _0.5Tl _0.5Ba ₂ (Ca ₃Nb ₁)Cu ₅O _14-δ and Cu _0.5Tl _0.5Ba ₂(Ca ₄Nb ₁)Cu ₆O _16-δ superconductors have been investigated. The Nb doping has been found to increase the oxygen contents in Cu _0.5Tl _0.5Ba ₂O _16-δ charge reservoir layer of the final compound. The post-annealing in the N ₂ atmosphere has been found to improve the superconducting properties; however, O ₂ annealing produced the material with inferior superconducting properties. The quantity of diamagnetism is increased with post-annealing in the nitrogen atmosphere; as N ₂ annealing helps in the formation of material with optimum carriers concentration in the CuO ₂ planes, which is done by the change in the charge state of thallium from Tl ³⁺ to Tl ¹⁺. The Nb substitution has been found to develop the higher CuO ₂ planner phases such as Cu _0.5Tl _0.5Ba ₂Can _-2Nb ₁Cun ₂ n+4-δ (n=5,6) with enhanced T _c's.