SUPERCONDUCTING PROPERTIES OF PB-FREE AND PB-SUBSTITUTED BULK CERAMICS OF BI-2212 CUPRATES

Superconducting properties of Pb-free and partially Pb-substituted bul k ceramics of the Bi2-xPbSr2CaCu2Oz system are studied under the influ ence 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 in tercalation of oxygen in the perovskite slabs, most probably resulting in the creation of localized carriers in form of Cu3+. The substituti on Pb-->Bi displays a beneficial role in the improvement of the superc onducting properties of the intergrain material of ceramics as well as in the creation of pinning centres with an optimal Pb concentration o f x=0.4. For this value the average distance of the Pb pinning centres of about 10 angstrom 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.