Enhancement in the high-Tc phase of BSCCO superconductors by Nb addition

Pure and Nb2O5 added Bi1.6Pb0.4NbxSr2Ca2Cu3Oδ superconductors (x varies up to 0.30) were synthesized by the solid state reaction method. Structural and superconducting properties of the samples were investigated. The fraction of the high-Tc phase (2223) increases with Nb addition up to x = 0.10, for which a nearly single 2223 phase was obtained. The critical temperature of the samples increases from 96 to 104 K with doping up to x = 0.20 and a further increase in Nb decreases the Tc sharply. Similarly, there is a considerable enhancement in the critical current density (jc) of the samples in the same doping range. Both AC susceptibility and transport measurements showed that the optimum Nb concentration is x = 0.20. The out-of-phase component of the AC susceptibility measurements showed that inter-grain coupling was enhanced up to the same doping level. Nb additions above x = 0.30 decrease the fraction of the high-Tc phase and degrade the superconducting properties. Present measurements indicate that x = 0.20 is the optimum Nb concentration in the BSCCO superconductor to enhance phase purity, inter-grain coupling and superconducting parameters (Tc and jc)