  Doping of MgB2 by nano-SiC and its potential for improvement of flux pinning
was studied for MgB2-x(SiC)x/2 with x = 0, 0.2 and 0.3 and a 10wt% nano-SiC
doped MgB2 samples. Co-substitution of B by Si and C counterbalanced the
effects of single-element doping, decreasing Tc by only 1.5K, introducing
pinning centres effective at high fields and temperatures and enhancing Jc and
Hirr significantly. Compared to the non-doped sample, Jc for the 10wt% doped
sample increased by a factor of 32 at 5K and 8T, 42 at 20K and 5T, and 14 at
30K and 2T. At 20K, which is considered to be a benchmark operating temperature
for MgB2, the best Jc for the doped sample was 2.4x10^5A/cm2 at 2T, which is
comparable to Jc of the best Ag/Bi-2223 tapes. At 20K and 4T, Jc was
36,000A/cm2, which was twice as high as for the best MgB2 thin films and an
order of magnitude higher than for the best Fe/MgB2 tapes. Because of such high
performance, it is anticipated that the future MgB2 conductors will be made
using the formula of MgBxSiyCz instead of the pure MgB2.
