Preparing MgB2 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 Jc improvement. In the other case, a two-step process was employed to make MgB2. Jc of the sample with the composition of MgB4 is very low after the first sintering. The Jc was dramatically improved after the second sintering, but Jc 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.