Influence of Ball-Milling Treatment of B Original Powder on the Phase Formation and Critical Current Density of Graphite Doped MgB$_{2}$

Abstract

In present work, the sintering process and superconducting properties of graphite doped MgB$_{2}$ prepared with milled B original powder were investigated. It is found that ball milling treatment of B original powder obviously suppresses the solid–solid reaction between Mg and B, whereas it enhances their liquid–solid reaction during the subsequent sintering process of these graphite doped MgB$_{2}$ bulks. Ball milling treatment of B original powder can also promote C substitution for B sites in MgB$_{2}$ crystal lattice in the graphite-doped samples, and thus obviously increase their values of $J_{c}$ at high fields. Moreover, ball milling also refines MgB$_{2}$ grains, enhancing grain boundary pinning and $J_{c}$ at high fields.