Sevenfold coordinated MgSe: experimental internal atom position determination to 146 GPa, diffraction studies to 202 GPa and theoretical studies to 500 GPa

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 ± 8 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