Carbon-Coating Layers on Boron Generated High Critical Current Density in MgB2 Superconductor.

Boron particles with a homogeneous carbon-coating layer were employed as the precursor to fabricate MgB2 superconductors to generate artificial two-dimensional (2D) flux-pinning centers. Systematic microstructure investigation reveals that the carbon layers are well-distributed in the MgB2 matrix without agglomeration. The thickness of the carbon layers is smaller than the MgB2 coherent length, which makes them transparent to supercurrent. The critical current density is increased because of the strong flux-pinning effects of the 2D carbon layers in the superconductor as highly efficient flux-pinning centers and the increased irreversibility field due to the carbon-doping effects.