Sevenfold Coordinated MgSe: Experimental Internal Atom Position Determination to 146 GPa, Diffraction Studies to 202 GPa, and Theoretical Studies to 500 GPa

Abstract

MgSe has been studied using energy dispersive x-ray diffraction to 202 GPa and local density approximation and ultrasoft pseudopotentials to 500 GPa. MgSe undergoes a ``continuous'' phase transformation from the rocksalt to FeSi ( $B28$) beginning at around $99\ifmmode\pm\else\textpm\fi{}8\mathrm{GPa}$ and approaching sevenfold coordination at 202 GPa. Theoretical computation finds the $B28$ transition beginning at 58 GPa followed by a transition to an orthorhombic distortion of the $B2$ structure at 429 GPa.