The effect of graphene coated Si, Ti and Nb additions on the superconducting properties of MgB₂ bulks

The effect of graphene (G) coated Si, Ti and Nb additions on the superconducting properties of MgB₂ was systematically studied. The additives were prepared by a coating process and all introduced powders were scattered and combined with graphene. The coating process was useful for the uniform distribution of additives in MgB₂ samples. The additives could effectively make the refinement of MgB₂ grain size, which achieved an enhancement of surface pinning. Meanwhile, the densities of all the doped samples were larger than those of pure samples, which ensured a better intergrain connection for supercurrent. Therefore, the critical current density of MgB₂ with 8 wt% G coated Nb addition got a significant enhancement due to the improvement of grain connectivity and flux pinning properties.