Doping effects of carbon and titanium on the critical current density of MgB2

MgB2 bulks doped with Ti or/ and C were prepared by an in situ solid state reaction method to determine the combined effect of C and Ti doping and to probe the detailed mechanism. The magnetization measurement shows that Mg-0.95Ti0.05B1.95C0.05 sample has significantly improved flux pinning compared to the MgB1.95C0.05 sample at 20 K, indicating that C and Ti are largely cooperative in improving the Jc( H) behaviour. No TiC phase was detected in the x- ray diffraction ( XRD) patterns. Moreover, the overlap of the ( 100) peaks of MgB1.95C0.05 and Mg0.95Ti0.05B1.95C0.05 showed that Ti doping does not reduce the amount of C in MgB2. Microstructural analyses revealed that the addition of Ti eliminated the porosity present in the carbon- doped MgB2 pellet, resulting in an improved intergrain connectivity and an increase of effective current pass. Further, MgB2 doped with C and Ti, which mainly consists of spherical grains about 200 - 300 nm in size, shows an higher grain homogeneity than the C- doped sample, suggesting that the Ti doping in MgB1- xCx has played an important role in obtaining uniform grains.