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 MgB(2). 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 (J(c)) valuewas 9.1 x 10(3) 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 J(c) improvement at high fields is attributed to the H(c2) enhancement caused by the increased disorder.