Effect of Ni doping on microstructure and superconductivity of MgB2 prepared by C - coated B powder

Abstract

The MgB2 bulk doped with Ni nanoparticles with a composition of (Mg1.05B2)Nix (x = 0, 0.04, and 0.06) has been prepared by an in-situ method using the carbon-coated amorphous boron powder as precursor. The combination influence of Ni and carbon doping on the microstructure and superconductivity of MgB2 sample has been clarified according to the XRD, DSC, SEM and PPMS measurements. It is found that the carbon-coated boron in the present work has benefited to the uniformly refined MgB2 grains, as well as a high level of homogeneous carbon doping in the MgB2 samples. The increased grain boundaries and efficient carbon institution of B has significantly enhanced the Jc (High magnetic field) in the MgB2 bulks due to the more pinning centers compared to the normal amorphous boron precursor. Moreover, it has found that the irreversibility field (Hirr) of MgB2 is greatly improved. However, the positive effect of carbon coated boron has been weakened by Ni doping at low magnetic field. Meanwhile, the formed eutectic liquid by Ni and Mg at 506℃has promoted activity of the C replacement of the B site in MgB2, which distorted the MgB2 grains and worsened the intergranular connectivity.