High critical current properties of MgB2 bulks prepared by a diffusion method

Highly dense MgB2 bulks with high purity were synthesized by the newly developed PICT-diffusion method, starting from magnesium and boron which were separately packed in sealed stainless tubes. Critical current density, Jc, systematically improved with a decrease of grain size of the samples. A sample reacted at 800°C for 60h exhibited the highest Jc of ∼0.86MA∕cm2 at 20K in self-field, which was almost three times higher than that of conventional porous MgB2 bulks prepared by the solid-state reaction. Besides an increase of effective current pass, small grains with 30–100nm in size and good grain connectivity resulted in the dramatically enhanced Jc.