Enhanced critical current density of MgB2 superconductor using a milled MgB4 precursor

Abstract

The synthesis of bulk MgB2 superconductors from Mg and MgB4 precursors instead of the conventional in situ process increases the packing density, but further enhancement of the critical current density is required. Herein, to improve the critical current density of bulk MgB2, the MgB4 precursor was subjected to planetary milling in toluene. The MgB4 powder was then mixed with Mg and heat-treated at 650 °C for 1 h to synthesize bulk MgB2. The microstructure, phases, and superconductivity of bulk MgB2 were investigated to determine the effect of MgB4 milling. MgB4 milling decreased the MgB2 grain size, and carbon incorporation from the milling solvent was observed, which caused the deterioration of the MgB2 crystallinity. These changes caused a reduction of the critical temperature; however, the critical current density was improved due to the increased magnetic flux pinning sites such as grain boundary and lattice distortion.