The effect of high-pressure synthesis on flux pinning in MgB2-based superconductors

Increasing the pressure during manufacturing MgB2 enhances the volume pinning force and moves the position of the maximum to higher magnetic fields. A similar shift was observed when Ti or SiC was added and the maximum of the volume pinning force was found at higher fields in in situ synthesized materials than in ex situ sintered samples. We attribute the observed changes to Mg-B-O oxygen-enriched regions and grains of higher magnesium borides in the MgB2 matrix. High-temperature processed materials demonstrated mainly point or mixed pinning while grain boundary pinning dominated after low-temperature synthesis.