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Sci Adv. 2018 Apr 25;4(4):eaao5864. doi: 10.1126/sciadv.aao5864. eCollection 2018 Apr.

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

Author information

1
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
2
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA.
3
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550, USA.
4
Division of Engineering and Applied Sciences, California Institute of Technology, 1200 E California Boulevard, Pasadena, CA 91125, USA.
5
Laboratory for Laser Energetics, Department of Physics and Astronomy, and Department of Mechanical Engineering, University of Rochester, Rochester, NY 14623-1299, USA.

Abstract

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.

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