Superconductivity of the bulk MgB(2)+nano(n)-SiC composite system: a high field magnetization study

We study the effect of nano(n)-SiC addition on the crystal structure, critical temperature (T(c)), critical current density (J(c)) and flux pinning in MgB(2) superconductors. X-ray diffraction patterns show that all the samples have MgB(2) as the main phase with a very small amount of MgO; further, with n-SiC addition the presence of Mg(2)Si is also noted and confirmed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The T(c) value for pure MgB(2) is 18.9 K under 8 T applied field, while it is 20.8 K for the 10 wt% n-SiC doped sample under the same field. This points towards the increment in the upper critical field value with n-SiC addition. The irreversibility field (H(irr)) for the 5% n-SiC added sample reached 11.3, 10 and 5.8 T, compared to 7.5, 6.5, and 4.2 T for the pure MgB(2) at 5, 10 and 20 K, respectively. The critical current density (J(c)) for the 5 wt% n-SiC added sample is increased by a factor of 35 at 10 K and 6.5 T field and by a factor 20 at 20 K and 4.2 T field. These results are understood on the basis of superconducting condensate (sigma band) disorder and ensuing intrinsic pining due to B-site C substitution clubbed with further external pinning due to available n-SiC/Mg(2)Si pins in the composite system.