Cooperative doping effects of Ti and C on critical current density and irreversibility field of MgB2

Carbon and titanium concurrently doped MgB2 alloys with a composition of Mg1−xTixB2−yCy have been prepared by an in situ solid state reaction method. The combination effects of carbon and Ti doping on structure, microstructure, irreversibility field (Hirr), and critical current density (Jc) of MgB2 have been investigated. It is found that doping Ti in MgB2 does not reduce the solubility of carbon in MgB2, but, on the contrary, it eliminates the porosity present in the carbon-doped MgB2, resulting in an improved intergrain connectivity. As a result, Jc and Hirr of MgB2 have been significantly improved, sharply contrasted to the situation of C-only-doped or Ti-only-doped MgB2 bulks. Our results clearly reveal that carbon and Ti codoping are largely cooperative in improving the performance of MgB2 in the high magnetic fields (>3T) and at high temperature (∼20K).