Flux pinning properties of impurity doped MgB2 bulks synthesized by diffusion method

Doping effects of carbon-containing impurities on the critical current properties and microstructure were systematically studied for highly dense MgB2 bulks prepared by the diffusion method starting from magnesium and boron which are separately packed in sealed stainless tubes. Obtained samples exhibited improved critical current density, Jc, simply by an increase of effective current pass. A non-doped MgB2 recorded almost double high Jc at 20 K compared with those of the conventional porous MgB2 bulks having ∼50% of the theoretical density, while irreversibility field, Hirr, did not largely change. Jc under high magnetic fields were enhanced by doping of carbon-containing impurities, such as SiC and B4C. Optimal doping levels of SiC and B4C for high critical current properties at 20 K are found to be ∼2% and 5%, respectively, as nominal carbon concentration at boron site. Difference in the optimal doping levels is originated from the difference in their reactivity.