Improvement of critical current density of MgB₂ bulk superconductor processed by Spark Plasma Sintering

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and optimization of the sintering kinetics and therefore makes it possible to obtain MgB₂ bulk superconductor with tailored microstructures consisting of grains with either spherical or elongated morphology. In this contribution, the role of the precursor powders on the superconducting properties of MgB₂ is investigated. Three sets of bulk MgB₂ material were processed from: (i) a commercially available MgB₂ powder; (ii) a mixture of Mg metal and amorphous B using a single-step solid-state reaction process and (iii) a mixture of amorphous boron coated with carbon and Mg metal. The samples were prepared in the same SPS processing conditions. The microstructure of the samples was investigated by X-ray diffraction, SEM and TEM and correlated to their superconducting properties. The critical current density of the best sample at 20K was J_c = 500 kA/cm² in self-field, which is one of the highest critical current density reported for MgB₂ bulk superconductors.