Superconducting properties of MgB2/Fe tape heavily doped with nanosized SiC

Abstract

The critical current density (Jc), upper critical field (Hc2)and irreversibility field (Hirr) have been investigated for powder-in-tube processedMgB2 tapes heavily doped with nanosized SiC up tox = 0.6 inMgB2+xSiC. We added nanosized SiC powders to the powder mixture ofMgH2 plus amorphousB and carried out Jc and resistivity measurements in magnetic fields up to 30 T at 4.2 K fortapes made from these mixtures. A maximum C substitution for B of∼3 at.% was obtained for 0.3 SiC addition. The value ofHirr at 4.2 K rose with increasing amounts of SiC addition, and a highestHirr of∼25.5 T wasobtained for x = 0.2–0.4 SiC-doped tapes. At 4.2 K and 8 T, the optimum addition level for obtaining the highestJc was in the 0.1 SiC-doped sample, while at 20 T the optimum addition level shifted toa 0.4 SiC-doped material. This shift can be explained by the enhancement ofHc2 and pinning effects of nanoparticles by the SiC addition. However, the highestlevels of SiC addition resulted in large amounts of impurity phases such asMg2Si and unreacted SiC. These impurities degrade the grain connectivity ofMgB2 andreduce Jc with increasing doping levels.