Abstract
The doping effect of Ti and Zr on the superconducting properties and the microstructure of sintered MgB2 bulk materials has been studied. The transition metal is found to work as a sintering assistant, which significantly enhances the grain connection of the MgB2 bulk materials during sintering processing. With this technique, we have fabricated Ti-doped MgB2 bulk materials consisting of fine 10 nm scale particles and achieved a high Jc over 1 MA/cm2 in 0 T at 20 K. The large enhancement of Jc is explained by the excellent connection between grains and a high density of pinning centers served by grain boundaries and MgO nanoparticles.