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

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 ten 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-7wt.%Si adopts the hexagonal close packed (hcp) structure over the measured pressure range, whereas Fe-15wt.%Si is observed in a body-centered cubic (bcc) 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 such planets.

Authors:
 [1];  [2];  [2];  [2];  [2];  [3];  [2];  [2];  [4]
  1. Princeton Univ., Princeton, NJ (United States); Johns Hopkins Univ., Baltimore, MD (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  4. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Univ., NJ (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP) (NA-10)
Contributing Org.:
Laboratory for Laser Energetics
OSTI Identifier:
1406024
Alternate Identifier(s):
OSTI ID: 1439048
Grant/Contract Number:  
NA0002720; NA0003611
Resource Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; high pressure; exoplanets; iron-silicon alloy; ramp compression

Citation Formats

Wicks, June K., Smith, Raymond F., Fratanduono, Dayne E., Coppari, Federica, Kraus, Richard G., Newman, Matthuew G., Rygg, J. Ryan, Eggert, Jon H., and Duffy, Thomas S. Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions. United States: N. p., 2018. Web. doi:10.1126/sciadv.aao5864.
Wicks, June K., Smith, Raymond F., Fratanduono, Dayne E., Coppari, Federica, Kraus, Richard G., Newman, Matthuew G., Rygg, J. Ryan, Eggert, Jon H., & Duffy, Thomas S. Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions. United States. doi:10.1126/sciadv.aao5864.
Wicks, June K., Smith, Raymond F., Fratanduono, Dayne E., Coppari, Federica, Kraus, Richard G., Newman, Matthuew G., Rygg, J. Ryan, Eggert, Jon H., and Duffy, Thomas S. Sun . "Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions". United States. doi:10.1126/sciadv.aao5864. https://www.osti.gov/servlets/purl/1406024.
@article{osti_1406024,
title = {Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions},
author = {Wicks, June K. and Smith, Raymond F. and Fratanduono, Dayne E. and Coppari, Federica and Kraus, Richard G. and Newman, Matthuew G. and Rygg, J. Ryan and Eggert, Jon H. and Duffy, Thomas S.},
abstractNote = {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 ten 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-7wt.%Si adopts the hexagonal close packed (hcp) structure over the measured pressure range, whereas Fe-15wt.%Si is observed in a body-centered cubic (bcc) 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 such planets.},
doi = {10.1126/sciadv.aao5864},
journal = {Science Advances},
number = 4,
volume = 4,
place = {United States},
year = {2018},
month = {4}
}

Journal Article:
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Cited by: 2 works
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Figures / Tables:

FIgure 1 FIgure 1: Experimental setup for laser ramp-compression experiments. (a) The laser drive is focused to an 800-µm spot on the front diamond surface of C/Au/C/Fe-Si/C or C/Fe-Si/LiF target packages, which are centered over a 300-µm diameter pinhole. (b) Ablation of the surface of the diamond pusher creates a rapidly expandingmore » plasma that launches a pressure wave through the pusher/sample/window interfaces. For the thin samples used in this experiment, reverberations within the Fe-Si alloy layer due to impedance mismatches across the boundaries rapidly equilibrates the pressure. (c) Schematic of the Powder X-ray Diffraction with Image Plates (PXRDIP) diagnostic. Quasimonochromatic X-rays emitted by a laser-generated plasma from a Cu, Fe or Ge foil (left: recorded X-ray emission spectra) diffract from the target package and are recorded by image plates that line the box interior. A rear aperture provides access for velocity interferometry (VISAR).« less

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