Stability of B2‐type FeS at Earth's inner core pressures

Using density functional theory, we investigated how substituting sulfur atoms for iron atoms affects the structure and energy of the body centered cubic and hexagonal close‐packed iron phases at 350 GPa and at 0 K. We conclude that formation of random (Fe,S) solid solutions is energetically favorable in all intermediate compositions, although the random low‐symmetry substitutions cause structural distortion. The (Fe,S) solid solution is nearly as favorable as the mechanical mixture of Fe‐hcp and FeS‐B2. This finding, in combination with dynamical stability, defines the B2 structure as a strong candidate for the sulfur‐bearing phase of the Earth's inner core. Key Points Negative values of the excess enthalpy and volume on the whole range of Fe‐S compositions for both bcc‐ and hcp‐structured solid solutions The dynamical stability of B2 FeS structure; this imply a possibility of crystallization of the B2 phase from the Fe‐S solid solution Higher enthalpies of FexSy structures with ordered sulfur distribution in comparison with disordered one