Mechanisms of the formation of a bulk superconducting phase MgB$_2$ at high temperatures

The structure of MgB$_2$ samples synthesized from magnesium flakes and a boron powder at temperatures of 900–1000$^\circ$C has been investigated. It has been found that the samples have “dendrite-like” and layered structures formed as a result of the dissolution of solid boron in liquid magnesium followed by crystallization. The obtained structures have been analyzed within the theoretical concepts of crystallization from melt.