The elastic properties of hcp-Fe alloys under the conditions of the Earth's inner core

• Published in: Earth and planetary science letters Vol. 493; pp. 118 - 127
• Main Authors: Li, Yunguo, Vočadlo, Lidunka, Brodholt, John P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-07-2018
• Subjects: AIMD; Earth's inner core; elasticity; iron alloys; Earth's inner core; AIMD; iron alloys; elasticity
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2018.04.013

Geophysical and cosmochemical constraints suggest the inner-core is mainly composed of iron with a few percent of light elements. However, despite extensive studies over many years, no single alloying light-element has been found that is able to simultaneously match the observed inner-core density and both seismic velocities. This has motivated a number of suggestions of other mechanism to lower velocities, such as anelasticity or premelting. However, an unexplored possibility is that a combination of two or more light-elements might produce the desired reduction in velocities and densities of the inner core. In order to test this, we use ab initio molecular dynamics calculations to map the elastic property space of hcp-Fe alloyed with S, Si and C at 360 GPa up to the melting temperature. Based on a mixing solid solution model together with direct simulations on the ternaries, we found a number of compositions which are able to match the observed properties of the inner core. This is the first time that the density, VP, Vs and the Poisson's ratio of the inner core have been matched directly with an hcp-Fe alloy.
•We have mapped the elastic property space of hcp-Fe–Si–S–C alloys at 360 GPa.•The hcp-Fe30Si1C1 was found satisfying the inner-core density and seismic velocities.•We also found other ternary and quaternary candidates based on a solid solution model.