Superconductivity of nano-TiO2-added MgB2

We report on the synthesis, phase formation, microstructure, and magnetization, of nano(n)-TiO2-added MgB2 polycrystalline compounds. The added n-TiO2 amounts are varied from 1% to 15% in weight (wt). All the studied samples are near single phase with small amounts of un-reacted Mg/MgO up to 10 wt%. The 15 wt% n-TiO2 added sample seems to be a multi-phase compound with unusual broadening of the main MgB2 reflection and additional unidentified lines in its X-ray diffraction (XRD) pattern. The superconducting transition temperature (Tc), as measured by magnetization experiments, decreases marginally with n-TiO2 addition, for example the Tcs are at 37.5 K and 35.5 K, respectively, for pristine and 10 wt% n-TiO2-added samples. This indicates that Ti has not significantly substituted into the host MgB2 lattice. The grain morphology of these compounds reveals porous regions and does not change much with TiO2 addition. High resolution transmission electron microscopy (HRTEM) studies revealed the presence of n-TiO2 in these samples. The critical current density (Jc) of the MgB2–n-TiO2 samples, as estimated using the Bean model, shows better performance under magnetic fields above 3 T than pristine MgB2 for up to 4 wt% of addition, and decreases rapidly for additions above 6 wt%. We conclude that n-TiO2 helps in enhancing the flux pinning centers in MgB2 superconductor and hence improves the Jc(H) performance for additions up to 4 wt% in fields above 3 T.