Conflicting Effects of SiC Doping on the Properties of Mechanically Alloyed Bulk ${\rm MgB}_{2}$

The influence of micro- and nano-scaled SiC on the phase formation, the structural properties, and the superconductivity of MgB₂ bulk samples was studied. Mechanical alloying was applied to prepare a nanocrystalline precursor powder with SiC additions up to 10 wt.%. The data implies that, in contrast to previously reported results in literature, the use of SiC as a dopant in MgB₂ shows a conflicting effect. Although a certain carbon substitution was observed and, therefore, H _c2 was enhanced, an often reported increase of J _c was only obtained for low SiC concentrations. Beyond that, a strong decline of J _c was observed, coming from an accumulation of SiC and Mg₂Si nanoparticles at the grain boundaries which decouples the grains and thereby decreases the connectivity and J _c.