SUPERCONDUCTIVITY OF NB-SUBSTITUTED BI-2223 SUPERCONDUCTOR

Superconductivity of Nb-doped samples of (BiPb)(2)Sr2Ca2Cu3Odelta has been investigated by substitution of this element at the Bi-site and t he Cu-site. While a depression of T-c with increasing dopant concentra tion is observed for both the series of samples, the effect is much mo re drastic for the Cu-site samples. Magnetic studies also show a more rapid increase in magnetisation of the Cu-site substituted samples. Th e results are explained on the possibility of formation of a virtual b ound state (VBS) of the d-level of Nb close to the E-F. (C) 1998 Elsev ier Science B.V. All rights reserved.