Abstract
The particle size, purity and form of the starting boron powdersplay an important role in the superconducting properties ofMgB2. Inthis paper high-purity (99.999%) boron powders with crystalline phase that were processed by ballmilling have been used as the precursor powders. It was observed that the critical current density(Jc) valuewas 9.1 × 103 A cm−2 at 5 K and 8 T, which is two times higher than for a sample withball-milled amorphous boron powders, and a factor of 40 higher than asample made from as-supplied amorphous boron powders. SignificantJc improvement at high fields is attributed to theHc2 enhancement caused by the increased disorder.
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