High Critical Current Density of Nanostructured MgB₂ Bulk Superconductor Densified by Spark Plasma Sintering

In situ MgB₂ 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 × 10⁵ A/cm² in the self-field and above 10⁴ A/cm² 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 MgB₂ nanograins in connection to the presence of MgO precipitates and areas rich in boron.