Effect of Carbon and SiC Doping on Microstructures of MgB2 Bulks and Wires by a Two-Step Reaction Method

Carbon and SiC doped MgB2 bulks and wires were fabricated by a two-step reaction method. The MgB4 samples were sintered at 900 °C for 2 h in closed argon atmosphere, and then an appropriate amount of Mg powder was mixed with the ground MgB4 powder to get MgB2 green compacts, which were sintered at 750 °C for 2 h to get bulk samples or at 680 °C for 2 h to get wire samples in closed argon atmosphere. Carbon or SiC doped MgB2 bulk samples were also prepared by conventional solid state sintering for comparison. The phase evolution and the microstructure of MgB2 samples were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The SEM results indicate that the compactedness and the dopant distribution homogeneity of MgB2 samples prepared by the two-step reaction method are improved obviously. The carbon doping can more effectively introduce the dopants into MgB2 crystalline lattice and grain boundaries compared with SiC doping.