High transport critical current density and largeHc2andHirrin nanoscale SiC doped MgB2wires sintered at low temperature

We report a systematic study on the effect of sintering temperature on the phase formation, critical current density, upper critical field and irreversibility field of nanoscale SiC doped MgB 2 . Bulk and Fe sheathed wires doped with different nano-SiC particle sizes have been made and heat treated at temperatures ranging from 580 to 1000 °C. A systematic correlation between the sintering temperature, normal state resistivity, RRR, J c , H c2 , and H irr has been found in all samples of each batch. Samples sintered at a lower temperature have a very fine and well consolidated grain structure while samples sintered at a high temperature contain large grains with easily distinguishable grain boundaries. Low temperature sintering resulted in a higher concentration of impurity precipitates, larger resistivity, higher J c up to 15 T and lower T c values. These samples show higher H c2 and H irr at T near T c but lower H c2 near T = 0 than samples sintered at high temperature. It is proposed that huge local strains produced by nano-precipitates and grain boundary structure are the dominant mechanism responsible for higher H c2 at T near T c . However, higher impurity scattering due to C substitution is responsible for higher H c2 in the low temperature regime for samples sintered at a higher temperature. In addition to high H c2 , it is also proposed that the large number of nano-impurities serve as pinning centres and improve the flux pinning, resulting in higher J c values at high magnetic fields up to 15 T.