Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions

• Published in: Science advances Vol. 4; no. 4; p. eaao5864
• Main Authors: Wicks, June K, Smith, Raymond F, Fratanduono, Dayne E, Coppari, Federica, Kraus, Richard G, Newman, Matthew G, Rygg, J Ryan, Eggert, Jon H, Duffy, Thomas S
• Format: Journal Article
• Language: English
• Published: United States AAAS 01.04.2018; American Association for the Advancement of Science
• Subjects: exoplanets; GEOSCIENCES; high pressure; iron-silicon alloy; Physics; Planetary Science; ramp compression; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.aao5864

The high-pressure behavior of Fe alloys governs the interior structure and dynamics of super-Earths, rocky extrasolar planets that could be as much as 10 times more massive than Earth. In experiments reaching up to 1300 GPa, we combine laser-driven dynamic ramp compression with in situ x-ray diffraction to study the effect of composition on the crystal structure and density of Fe-Si alloys, a potential constituent of super-Earth cores. We find that Fe-Si alloy with 7 weight % (wt %) Si adopts the hexagonal close-packed structure over the measured pressure range, whereas Fe-15wt%Si is observed in a body-centered cubic structure. This study represents the first experimental determination of the density and crystal structure of Fe-Si alloys at pressures corresponding to the center of a ~3-Earth mass terrestrial planet. Our results allow for direct determination of the effects of light elements on core radius, density, and pressures for these planets.