Superconducting properties of Pb-free and Pb-substituted bulk ceramics of Bi-2212 cuprates

Abstract

Superconducting properties of Pb-free and partially Pb-substituted bulk ceramics of the Bi 2- x Pb x Sr 2CaCu 2O z system are studied under the influence of various methods of post-treatment. It is shown that the shift of T c from the maximum of about 95 K to lower values is due to an intercalation of oxygen in the perovskite slabs, most probably resulting in the creation of localized carriers in form of Cu 3+. The substitution Pb→Bi displays a beneficial role in the improvement of the superconducting properties of the intergrain material of ceramics as well as in the creation of pinning centres with an optimal Pb concentration of x=0.4. For this value the average distance of the Pb pinning centres of about 10 Å correlates with the coherence length of 2212 in the a-b plane. As possible pinning centres lattice defects created by the intergrowth of 2223 in 2212 are considered.