High Critical Current Density of Nanostructured MgB 2 Bulk Superconductor Densified by Spark Plasma Sintering.

In situ MgB 2 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 c , which was measured at 20 K. Extremely high critical current densities of up to 6.75 × 10 5 A/cm 2 in the self-field and above 10 4 A/cm 2 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 2 nanograins in connection to the presence of MgO precipitates and areas rich in boron.