CRITICAL-CURRENT DENSITY IN SINTERED HIGH-TC (BI, PB)-SR-CA-CU-OXIDE

Two samples, once and twice sintered, of a multiphase high-Tc superconducting Bi1.8Pb0.2Sr2Ca2Cu3Oy compound were studied through AC magnetic susceptibility and electrical resistivity measurements. Using the critical-state model, the intergranular critical-current density is calculated from the AC susceptibility data. In contrast with the single-phase YBa2Cu3Ox compound, the coupling between superconducting grains is more complex in this case. For the once sintered sample, the susceptibility data show that there is some kind of strong coupling (a few orders of magnitude stronger than the ordinary intergranular coupling) within the clusters of high-Tc superconducting grains, but the coupling between the clusters is rather weak. The procedure of repeated grinding and sintering breaks the coupling in the clusters, but substantially improves the coupling in the whole sample, yielding an increase of the critical-current density by a factor of above 6. © 1990.