Abstract:

The grain boundaries (GB) in polycrytalline High-Tc materials constitute a limitation for the use of these materials in several devices. In order to avoid undesirable features of GB, we have used the Spark Plasma Sintering (SPS) method for produce polycrystalline samples of Bi1:65Pb0:35Sr2Ca2Cu3O10+ (Bi-2223). The high heating rate and short dwell times, which are specific to the SPS technique can reduce the GB influence on functional properties of the Bi-2223. We have studied a set of samples sintered at different consolidation temperatures Td, ranging from 750 to 830◦C. The samples were found to have densities close to 90% of the theoretical value and an expected relatioship between Td and the deoxygenation of the samples because the SPS process occurs under vacuum. We have also found that the oxygen content of the samples can be restored by post-annealing, a heat treatment made in air, at 750 ◦C for only 5 min. Such a heat treatment has a definite effect on the general properties of the samples, including the GB features, as an improvement of their transport and magnetic properties occurs. We show some aspects of the microstructure of the Bi-2223 ceramics made by the SPS method. Finally, after the post-annealing treatment and the enhancement of the microstructure, transport and magnetic properties, the samples become viable to building devices as the superconducting fault current limiters (SFCL).