Effects of morphology of Mg powder precursor on phase formation and superconducting properties of Mg11B2 low activation superconductor

Abstract

The effect of morphology with magnesium (Mg) powder on phase formation and critical current density (J_c,) of sintered Mg¹¹B₂ bulk was studied. As a precursor for the formation of Mg¹¹B₂, the morphology of spherical and plate-like of Mg powder were separately synthesized using atomization and chemical reduction methods. From differential thermal analyses of the sintering process, the solid–solid reaction of a Mg¹¹B₂ sample using spherical Mg powder was confirmed to be much weaker than the plate-like one, and the second exothermic peak place was shifted back and its intensity was increased due to a special microstructure of spherical Mg powder. XRD analysis of Mg¹¹B₂ samples showed that the volume fraction of Mg¹¹B₂ in the sintered sample with plate-like Mg was higher than that with the spherical one, and for all the samples MgB₂ is the main phase. The Mg¹¹B₂ sample using spherical Mg powder had two different kinds of microstructures because of differences in their diffusivity and their contact interfaces. The J_c value of an Mg¹¹B₂ sample using spherical Mg powder enhanced the entire field; it was twice as high as that using plate-like Mg, and it was even better than all the J_c values reported in previous literature using the same kind of Mg powder as precursor.