Thermo-physical properties of body-centered cubic iron–magnesium alloys under extreme conditions

Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron–magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi–Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C′C′). Magnesium alloying significantly increases C′C′ of Fe, and bcc Fe–Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe–Mg alloy with 5% Mg agree well with those of the Earth’s inner core as provided by seismic observations.

Research highlights
► At the conditions of the Earth’s inner core, Mg stabilizes bcc iron dynamically.
► Fe0.95Mg0.05 reproduces the physical properties of the inner core.
► A bcc structured Fe–Mg alloy is a strong candidate model of the inner core.