Significant improvement of Jc in MgB2 bulk superconductor using ball-milled high-purity crystalline boron

The particle size, purity and form of the starting boron powders play an important role in the superconducting properties of MgB2. In this paper high-purity (99.999%) boron powders with crystalline phase that were processed by ball milling have been used as the precursor powders. It was observed that the critical current density (Jc) value was 9.1 x 103 A cm-2 at 5 K and 8 T, which is two times higher than for a sample with ball-milled amorphous boron powders, and a factor of 40 higher than a sample made from as-supplied amorphous boron powders. Significant Jc improvement at high fields is attributed to the Hc2 enhancement caused by the increased disorder.