Comparison of carbon-doped MgB2 bulks fabricated from pre-synthesized Mg/CNT and Mg/amorphous carbon composites
MgB2 samples containing 2.5 wt% multi-walled carbon nanotubes (CNTs) and amorphous carbon (nano-C) were sintered at 800 C. The doped samples were prepared from Mg/CNT and Mg/nano-C composites, which were previously synthesized from coarse Mg and fine Mg by chemical vapor deposition, respectively. We made comparisons between the two samples on the C-doping level, the MgO contents, and the effects of the carbon source on critical current density (J c) by investigating the phase composition, microstructure, and magnetic properties. Compared with pure MgB2 (coarse Mg), the J c performance at high field was improved in the CNT-doped sample (coarse Mg) due to the high C substitution level induced lattice defects as pinning centers. However, J c values of the amorphous C-doped sample with sufficient C doping decreased over the entire field in contrast with the pure sample (fine Mg), which exhibited the highest J c performance among the samples. This is attributed to the much more MgO impurities, mostly generated during the preparation of Mg/C composites, than the CNT-doped sample. 2013 Springer-Verlag Berlin Heidelberg.