Phase evolution and microstructure of highJ_cSiC doped MgB₂fabricated by hot pressing

We report the phase evolution, microstructure, and critical current density (J(c)) of the SiC doped MgB2 superconductors. In our study, all samples were fabricated by hot pressing with a heating rate of 200 degrees C min(-1). The results show that the reaction of 2Mg + SiC = Mg2Si + C can occur at about 500 degrees C, about 50 degrees C lower than the formation temperature of MgB2. On the other hand, according to the experimental results and thermodynamic calculations, boron (B) does not react with SiC to form B4C and Si, neither does MgB2 react with SiC to form Mg2Si and B4C. The MgB2 phase was formed via both a solid-solid reaction (during the heating process between about 500 and 650 degrees C) and a liquid-solid reaction (> 650 degrees C) after the melting of Mg, and the two reactions resulted in differences in the grain size of the MgB2. From scanning electron microscopy, the Mg2Si particles are homogeneously distributed within the MgB2 matrix, with particle sizes ranging from 35 to 230 nm. From the perspective of superconductivity, the C substitution results in strong electron scattering centers in the MgB2 structure. It reduces the electron mean free path and thus may significantly enhance the magnetic J(c). The peak J(c) of the 5 wt% SiC doped MgB2 reaches above 10(6) A cm(-2) at 5 K, and decreases slowly with increasing field, remaining high, above 10(5) A cm(-2), at 7 T.