Preparation and Characterization of Mg 1− x B 2 Bulk Samples and Cu/Nb Sheathed Wires with Low Grade Amorphous Boron Powder

MgB 2 bulk and wire samples were prepared using cheap, low grade amorphous boron powders. Based on chemical analysis performed on the starting reagents, three nominal stoichiometries were studied. It was found that the structural and superconducting properties of the bulk samples were not affected by the composition, but that residual Mg was left in the wires for the nominal MgB 2 composition. In contrast, slightly Mg-deficient compositions were free from residual Mg and exhibited higher critical current densities. The MgB 2 phase formation kinetics was not influenced by the variations in the nominal powder composition.