The fabrication of graphene supported Ni nanoparticles and its doping influence on the microstructure and superconductivity of MgB2

A highly dispersed Ni nanoparticle supported on a graphene matrix (nano-Ni/G) has been successfully synthesized using a novel chemical reduction process to overcome agglomeration in traditional MgB₂ preparation methods. The influence of the reduction technique on nanoparticle size and structure was thoroughly investigated using a model system. The resulting nanoparticles were small enough (10 nm) to decorate the 2D graphene layers as sandwich structures. This unique morphology contributes to providing more effective flux pinning centers by forming tiny MgNi_2.5B₂ and efficiently substituting C for B in MgB₂ bulks through the principle of double action. Moreover, the low-melting eutectic liquid formed by Mg-Ni at 506 °C is beneficial for the fast fabrication of well-connected MgB₂ at low temperatures. Furthermore, a small enhancement of critical current density (J_c) was observed in the doped sample with respect to the undoped ones. However, the advantages of the as-prepared nanoparticles were greatly suppressed by the large presence of MgO during the deposition process, leading to lower superconducting performance than undoped MgB₂ bulks. Based on the analysis, further investigation should focus on inducing more flux pinning centers by controlling impurities during the deposition process for achieving optimal performance.