Preparing ${\rm MgB}_{2}$ With Excessive Mg Environment Sintering and Two-Step Sintering Approach

MgB₂ superconductors were made with two processes in this work. In one case, the SiC doped MgB₂ pellets were sintered in excessive Mg medium. It is found that the samples sintered in excessive Mg medium present Mg-rich composition comparing with the one sintered in Ar gas. The density is higher and the resistance is lower due to the penetration of the Mg into the pores and grain boundary of MgB₂, which is beneficial to the J_c improvement. In the other case, a two-step process was employed to make MgB₂. J_c of the sample with the composition of MgB₄ is very low after the first sintering. The J_c was dramatically improved after the second sintering, but J_c of the two-step made sample is still poorer than the MgB₂ made with general one step sintering due to the connectivity deterioration caused by the pulverization prior to the second sintering.