Enhancement of grain connectivity and critical current density in the ex-situ sintered MgB2 superconductors by doping minor Cu

The influence of Cu addition on the microstructure and superconducting performance of ex-situ sintered MgB2 is systemically studied. It is found that the critical current density (J(c)) of the Cu-doped sample is improved compared to the un-doped samples. In particular, the J(c) of the Cu-doped sample sintered at 900 degrees C for only 10 min is the best value at low fields. The reason is that Cu addition can obviously promote the decomposition of MgB2 MgB2 + Mg, which produces more Mg that can then react with Cu, forming local Mg-Cu liquid at high temperature. The presence of this local Mg-Cu liquid can significantly enhance the migration and self-sintering of MgB2, leading to the significant improvement in the grain connectivity and J(c). Our results indicate that Cu addition is a promising method to fabricate high-performance ex-situ MgB2 bulks and wires. (C) 2017 Elsevier B.V. All rights reserved