Effect of grain size and doping level of SiC on the superconductivity and critical current density in MgB2 superconductor

SiC doped MgB₂ polycrystalline samples were fabricated by in-situ reaction using different grain sizes (20 nm, 100 nm, and 37 μm) of SiC and different doping levels (0, 8, 10, 12, 15 wt%). Phases, microstructures, superconductivity, critical current density and flux pinning have been systematically investigated using XRD, SEM, TEM, and magnetic measurements. Results show that grain sizes of the starting precursors of SiC have a strong effect on the critical current density and its field dependence. The smaller the SiC grains are, the better the J_c field performance is. Significant enhancement of J_c and the irreversibility field H_irr were revealed for all the SiC doped MgB₂ with additions up to 15 wt%. A J_c as high as 20,000 A/cm² in 8 Tesla at 5 K was achieved for the sample doped with 10 wt% SiC with a grain size of 20 nm. Results indicate that the nano-inclusions and substitution inside MgB₂ are responsible for the enhancement of flux pinning.