An ab initio study of S-substituted iron–nickel–silicon alloy at the Earth's inner core pressure

Abstract

The thermodynamic stability of S-substituting Si into a bcc Fe_0.80Ni_0.05S _x Si_(0.15−x) random alloy, with x=0.025 n (n=0−− 4), was investigated up to 350 GPa by using an ab initio density functional method based on the full charge density–exact muffin-tin orbital–coherent potential approximation scheme. From the analysis of the calculated Δ H values, we suggest that the FeNiSSi stoichiometry with zero sulphur content always behaves as the most stable system along the whole pressure range of 0–350 GPa. As a general tendency, we found that the alloys with 6.8–8.1 wt.% Si are energetically more stable than those with lower silicon content, thus supporting the dissolution mechanism for the Earth's inner core compositional model.

Keywords:

• Earth's core composition
• high-pressure
• FeNiSSi alloys
• DFT
• EMTO
• CPA

Acknowledgements

The authors acknowledge financial support by the European Mineral Sciences Initiative (EuroMinScl) of the European Science Foundation, the Spanish Ministry of Education and Science (Ramón y Cajal program and CGL2008-00891), the Universidad Complutense de Madrid and Comunidad Autónoma de Madrid (CG 07-UCM/AMB/-2397), the Swedish Research Council, the Swedish Foundation for Strategic Research, and the Hungarian Scientific Research Fund (T046773 and T048827). One of the authors (M. Mattesini) also wishes to acknowledge the Aula SUN Microsystems of the Universidad Complutense de Madrid for use of computer power.