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 the 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, resulting 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 induced by Ti doping are distributed in the MgB2 matrix, and this may play an important role in flux pinning enhancement. (C) 2001 American Institute of Physics.