A Novel Approach for Efficient Ni Nanoparticle Doping of MgB $_{\bf 2}$ by Liquid-Assisted Sintering

Ni nanoparticles were successfully introduced for preparing polycrystalline MgB ₂ samples by a novel reduction method. According to transmission electron microscopy, the obtained Ni nanoparticles with average grain size of 5 nm are distributed in the B matrix without agglomeration. The missing shift in X-ray diffraction peaks indicates that Ni nanoparticles could not substitute Mg sites in the lattice, but rather form the ternary compound MgNi_2.5B₂ above 600°C. The low-melting eutectic liquid formed by Mg-Ni at 506°C is responsible for the formation of plate-like MgB₂ grains and the fast fabrication of MgB₂ at low temperature. The sample doped with nano-Ni has better grain connectivity and the critical current density (Jc) with respect to the commercial Ni-doped sample, but there is no improvement compare with the pure MgB₂ sample. A sintering model was accounted for understanding the reaction between Mg and B with the assistance of Ni nanoparticles.