Study of structural properties of Fe and FeS at conditions of Earth’s inner core

The observation of seismic waves, composition of meteorites, experimental and computational results of materials at extreme conditions indicate that the Earth's core (320-350GPa and 5000-6500K) is composed mostly of Fe with a less presence of light elements such as Si, C and S of high solubility at these conditions. The inclusion of these elements may explain the difference in density that exists between seismic data and relevant laboratory results. We have performed computational calculations based on functional density theory (DFT) to study structural, magnetic and thermodynamic properties of Fe pure phases at Earth’s inner core conditions and so obtain information on thermodynamic stability. We found the hcp phase to be the most stable at inner core conditions as has been reported by many previous works (Alfe et al., 2015, Denoeud et al., 2016). Since S is one of the candidates to be incorporated into the core, this study analysis several solid phases of FeS as well as several liquid and solid solutions of FeS alloys ranging from a S concentration (3.7wt%-16wt%) In the case of solid FeS we found troilite (NiAs) to be the most stable phase at ambient conditions whereas at core conditions a CsCl becomes stable.