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

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