Infiltration effect of Mg with different matter states in the reaction of MgB₂ bulks

MgB₂ superconductor bulks were fabricated using Mg and B precursors. The physical state of Mg (solid, liquid, or gas) significantly influences the final product, MgB₂ bulk. In this study, the Solid-Solid, Liquid-Solid, and Gas-Solid methods were employed to fabricate MgB₂ bulks. The superconducting properties and microstructure of various samples were systematically investigated. Notably, for the first time, nano-CT was utilized to comprehensively and non-destructively analyze the microstructure of MgB₂ bulks, particularly the size and distribution of voids, which serve as the primary barrier affecting the superconducting properties. By examining the microstructure characteristics, the infiltration effect of Mg in different physical states during the reaction was analyzed, and a feasible reaction model was established. This research contributes to a better understanding of the reaction mechanism of MgB₂, which may aid other researchers in enhancing the properties of MgB₂ superconductors.