Comparison of Critical Current Density in Undoped, Glycine-doped, and Cu-and-Glycine-Co-doped MgB₂ Synthetized from nm-Boron and μm-Boron

Nano-boron (800 nm) and μm-boron (25 μm) precursor were used to synthetize glycine-doped, Cu-and-glycine-co-doped, and undoped MgB₂ samples at 800 ^∘C. The C substitution level caused by glycine doping, the MgO content, and the full width at half maximum of the (101) peak for MgB₂ phase were compared to evaluate the critical current density (J_c) of the six samples. The undoped sample from the nm-boron powder showed enhanced J_c over the entire field in contrast with those from 25-um boron, since the excess MgO in nm-boron prepared sample serves as effective pinning centers. On the contrary, due to the reduced MgO pinning centers as well as the increase of the grain size, the glycine-doped nm-boron sample only enhanced the J_c performance in the high-field region (H>4.5 T), while the low-field J_c values showed a considerable decrease. For the Cu-and-glycine-co-doped sample, the J_c performance is nearly without regard to the size of the boron precursor as the high-field J_c of the nm-B sample decreased a little, while the low-field J_c remained at the same level as that of the μm-B sample.