Microstructure and superconducting property research of Cu-Mg reinforcing graphene and grain refining MgB2 by carbon-contained substances doping

We report the C substitution effects in MgB 2 bulks on the lattice parameters, FWHM, and critical current density ( J c ) as a function of doping level. It is shown that using carbon-coated boron powder can effectively control the grain growth of MgB 2 during the whole sintering process. Accompanied by the rapid cooling process, the final average grain size can be restrained within merely 50 nm, and the J c value of the sample can be significantly improved at high field. On top of that, adding Cu is also considered a key factor in improving the current carrying property of the graphene-doped sample throughout the whole field, which can be attributed to the formation of the MgCu 2 alloy phase.