Interplay between boron precursors and Ni-Co-B nanoparticle doping in the fabrication of MgB2 superconductor with improved electromagnetic properties

The influence of different boron precursor powders on the critical current density of MgB2 superconductor with added Ni-Co-B nanoparticles is investigated. Different types of boron have different morphologies, particle sizes and impurity content, all of which have a strong impact on the critical current density (Jc). The boron samples investigated in this study include three different boron powders: semicrystalline boron (denoted as SC), with nanosized particles and high purity (99%) supplied from Specialty Materials, Inc. (USA); amorphous boron (denoted as AB), with nanosized particles and high purity (99%) supplied from Russia; and finally pure crystalline boron (denoted as CB), with micron-sized particles and 96% purity supplied from Tangshan WeiHao (China). The MgB2 samples made from AB showed the best improvement of critical current with 2.5 wt.% Ni-Co-B doping; Jc was above 100,000 A cm−2 at 4 T and 5 K. Under the same conditions, Jc for MgB2 made from SC was slightly worse than for the MgB2 made from AB, ∼100,000 A cm−2. On the other hand, MgB2 made from CB presented sharply reduced Jc with Ni-Co-B doping at both measured temperatures, 5 K and 20 K.