Spark plasma sintering consolidation of Bi_1.65Pb_0.35Sr₂Ca₂Cu₃0_10+δ ceramic samples

Pre-reacted powders of (Bi-Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at different consolidated temperatures T_D. We have found that the transport properties of SPS samples depend on their oxygen content because the SPS process is performed under vacuum. From these results we have inferred that SPS samples are oxygen deficient and that a post-annealing treatment, performed in air for a brief time interval, is needed to restore such a deficiency. Measurements of temperature dependence of the thermal conductivity, κ(T), were performed in all SPS samples including a reference sample sintered at 845 °C in air. The results indicate that the electronic contribution to the thermal conductivity in all samples is very low. Values of κ were found to be higher in SPS samples mostly because of their high volume density of ~ 5.7 g/cm³. We have also performed measurements of the critical current density as a function of the applied magnetic field, J_c(B_a). All samples display a clear Josephson-like behavior and low values of the superconducting critical current density at zero applied magnetic field. The experimental results indicate that the oxygen deficiency in SPS samples is marked near the grain boundaries. This suggests the occurrence of grains with core-shell morphology, where the width of the shell is consolidation temperature dependent.