Properties of pure and carbon sphere doped MgB2 prepared from low grade boron powders

Low grade boron powders were used to fabricate pure and submicron-sized carbon sphere doped MgB2 superconductor. The boron powders used showed low reactivity towards MgB2 formation, as compared to high purity (99%) amorphous boron, which might result from the larger grain size, and the existence of crystalline boron or boron oxide in the former. However, the samples prepared from this boron powder showed comparable Jc values at 20 K and in low field (T) to those from a sample prepared from the high quality boron. Doping submicron-sized carbon spheres had successfully introduced carbon substitution for boron, and so improved the Hc2, Hirr, and in-field Jc properties of MgB2.