The effect of Cu addition on the phase formation and critical current density in the sugar Doped MgB2 superconductor
With the aim of improving the critical current density (J c) in theMgB 2 superconductor, minor Cu (3 at%) was doped to the MgB 2 samples in-situ sintered with Mg powder and sugar-coated amorphous B powder. Combined with thermal analysis, phase identification, microstructure observation and J c measurement, the effect of minor Cu addition on the sintering mechanism, microstructure and critical current density of sugar-doped MgB 2 superconductors were investigated. It is found that the minor Cu addition could obviously accelerated the MgB 2 phase formation and improve the growth ofMgB 2 grains during the sintering process of sugar-doped MgB 2 due to the appearance of Mg-Cu liquid at low sintering temperature. On the other hand, the Mg-Cu liquid hindered the reactive C released from sugar entering in the MgB 2 crystal lattice. Hence, the connectivity between MgB 2 grains was improved accompanying with the C substitution for B is decreased. At 20 K, the J c of codoped samples at low fields was further increased whereas it is decreased at high fields, compared with the only sugardoped samples. Springer Science+Business Media, LLC 2012.