High Critical Current Density of Nanostructured MgB Bulk Superconductor Densified by Spark Plasma Sintering.

In situ MgB superconducting samples were prepared by using the spark plasma sintering method. The density of the obtained bulks was up to 95% of the theoretical value predicted for the material. The structural and microstructural characterizations of the samples were investigated using X-ray diffraction and SEM and correlated to their superconducting properties, in particular their critical current densities, J, which was measured at 20 K. Extremely high critical current densities of up to 6.75 × 10 A/cm in the self-field and above 10 A/cm at 4 T were measured at 20 K, indicating that vortex pinning is very strong. This property is mainly attributed to the sample density and MgB nanograins in connection to the presence of MgO precipitates and areas rich in boron.