Consolidation of Bi-2223 superconducting powders by spark plasma sintering Available to Purchase

The spark plasma sintering (SPS) technique, by using a compacting pressure of 50 MPa, was used to consolidate pre-reacted powders of $Bi1.65Pb0.35Sr2Ca2Cu3O10+δ$ (Bi-2223). The influence of the consolidation temperature, $TD$⁠, on the structural and electrical properties has been investigated and compared with those of a reference sample synthesized by the traditional solid-state reaction method and subjected to the same compacting pressure. From the X-ray diffraction patterns, performed in both powder and pellet samples, we have found that the dominant phase is the Bi-2223 in all samples but traces of the $Bi2Sr2CaCu2O8+x$ (Bi-2212) were identified. Their relative density were $∼85 %$ of the theoretical density and the temperature dependence of the electrical resistivity, $ρ(T)$⁠, indicated that increasing $TD$ results in samples with low oxygen content because the SPS is performed in vacuum. Features of the $ρ(T)$ data, as the occurrence of normal-state semiconductor-like behavior of $ρ(T)$ and the double resistive superconducting transition, are consistent with samples comprised of grains with shell-core morphology in which the shell is oxygen deficient. The SPS samples also exhibited superconducting critical current density at 77 K, $Jc(77K)$⁠, between 2 and 10 $A/cm2$⁠, values much smaller than $∼ 22 A/cm2$ measured in the reference sample. Reoxygenation of the SPS samples, post-annealed in air at different temperatures and times, was found to improve their microstructural and transport properties. Besides the suppression of the Bragg peaks belonging to the Bi-2212 phase, the superconducting properties of the post-annealed samples and particularly $Jc(77K)$ were comparable or better than those corresponding to the reference sample. Post-annealed samples at $750 °C$ for 5 min exhibited $Jc(77K) ∼130 A/cm2$ even when uniaxially pressed at only 50 MPa.