High critical current density of MgB2 bulk superconductor doped with Ti and sintered at ambient pressure

Ti-doped MgB2 superconductors with different doping levels were prepared by solid-state reaction at ambient pressure. The density, diamagnetic signal, and J(c) of the samples change significantly with the doping level, with t he best result achieved at x=0.1. At 5 K, the J(c) reaches 2x10(6) A/cm(2) in the self-field and 5x10(4) A/cm(2) in 5 T. At 20 K, the J(c) is still as high as 1.3x10(6) A/cm(2) in the self-field and 9.4x10(4) A/cm(2) in 2 T. It is observed that partial melting occurs in the Ti-doped samples, resulti ng in an excellent grain connection and extremely high density. In addition , some fine particles (with sizes from 10 to 100 nm) of the second phases i nduced by Ti doping are distributed in the MgB2 matrix, and this may play a n important role in flux pinning enhancement. (C) 2001 American Institute o f Physics.