Negative effects of crystalline-SiC doping on the critical current density in Ti-sheathed MgB2(SiC)ysuperconducting wires

Ti-sheathed MgB2 wires doped with nanosize crystalline-SiC up to a concentration of 15?wt% SiC have been fabricated, and the effects of the SiC doping on the critical current density (Jc) and other superconducting properties studied. In contrast with the previously reported results that nano-SiC doping with a doping range below 16?wt% usually enhances Jc, particularly at higher fields, our measurements show that SiC doping decreases Jc over almost the whole field range from 0 to 7.3?T at all temperatures. Furthermore, it is found that the degradation of Jc becomes stronger at higher SiC doping levels, which is also in sharp contrast with the reported results that Jc is usually optimized at doping levels near 10?wt% SiC. Our results indicate that these negative effects on Jc could be attributed to the absence of significant effective pinning centres (mainly Mg2Si) due to the high chemical stability of the crystalline-SiC particles.