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Title: High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys

Abstract

The Earth's iron-dominant core is known to contain nickel from cosmochemical analysis and some amount of light elements from geophysical constraints on density and seismic wave velocities. Although there have been several studies to constrain thermoelastic properties of iron-alloys, there has been no systematic study on the effects of nickel and light elements on properties of iron using the same experimental methods and data analysis approach. We conducted nuclear resonant inelastic X-ray scattering and X-ray diffraction experiments on body-centered cubic and hexagonal close-packed (hcp) Fe 0.91Ni 0.09 and Fe 0.8Ni 0.1Si 0.1 up to 104 GPa and 86 GPa, respectively, and compare to similar measurements conducted on hcp-Fe up to 171 GPa. Specifically, we determine the Debye sound velocity from the low-energy transfer region of the (partial) phonon density of states (DOS) using the equation of state determined for each material and a new approach which utilizes information criteria and probability distributions. Nickel decreases the shear velocity of iron, while 10 at% Si has little to no effect on the shear velocity of Fe 0.91Ni 0.09. We observe that the shape of the phonon DOS of these alloys remains similar with increasing pressure. In the measured compression range, we thereforemore » apply a generalized scaling law to describe the volume dependence of the phonon DOS and find that the vibrational Grüneisen parameters of hcp-Fe 0.91Ni 0.09 are nearly indistinguishable from those hcp-Fe and those for Fe 0.8Ni 0.1Si 0.1 trend lower. From the vibrational free energy, we constrain the harmonic vibrational component of thermal pressure, which shows a significant positive deviation from theoretical calculations of hcp-Fe at pressures and temperatures of Earth's core. Collectively, our results demonstrate that the effects of nickel should be considered when modeling iron-rich planetary cores.« less

Authors:
ORCiD logo [1];  [2];  [2];  [3];  [3]
  1. California Inst. of Technology (CalTech), La Canada Flintridge, CA (United States). Seismological Lab.; Exxon Mobil, Spring, TX (United States)
  2. California Inst. of Technology (CalTech), La Canada Flintridge, CA (United States). Seismological Lab.
  3. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); W.M. Keck Foundation, Los Angeles, CA (United States); USDOE Office of Science (SC)
OSTI Identifier:
1559451
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Physics of the Earth and Planetary Interiors
Additional Journal Information:
Journal Volume: 294; Journal Issue: C; Journal ID: ISSN 0031-9201
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Earth’s core; Grüneisen parameter; high pressure; nuclear resonant inelastic x-ray spectroscopy; sound velocity

Citation Formats

Morrison, Rachel A., Jackson, Jennifer M., Sturhahn, Wolfgang, Zhao, Jiyong, and Toellner, Thomas S. High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys. United States: N. p., 2019. Web. doi:10.1016/j.pepi.2019.05.011.
Morrison, Rachel A., Jackson, Jennifer M., Sturhahn, Wolfgang, Zhao, Jiyong, & Toellner, Thomas S. High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys. United States. doi:10.1016/j.pepi.2019.05.011.
Morrison, Rachel A., Jackson, Jennifer M., Sturhahn, Wolfgang, Zhao, Jiyong, and Toellner, Thomas S. Sun . "High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys". United States. doi:10.1016/j.pepi.2019.05.011.
@article{osti_1559451,
title = {High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys},
author = {Morrison, Rachel A. and Jackson, Jennifer M. and Sturhahn, Wolfgang and Zhao, Jiyong and Toellner, Thomas S.},
abstractNote = {The Earth's iron-dominant core is known to contain nickel from cosmochemical analysis and some amount of light elements from geophysical constraints on density and seismic wave velocities. Although there have been several studies to constrain thermoelastic properties of iron-alloys, there has been no systematic study on the effects of nickel and light elements on properties of iron using the same experimental methods and data analysis approach. We conducted nuclear resonant inelastic X-ray scattering and X-ray diffraction experiments on body-centered cubic and hexagonal close-packed (hcp) Fe0.91Ni0.09 and Fe0.8Ni0.1Si0.1 up to 104 GPa and 86 GPa, respectively, and compare to similar measurements conducted on hcp-Fe up to 171 GPa. Specifically, we determine the Debye sound velocity from the low-energy transfer region of the (partial) phonon density of states (DOS) using the equation of state determined for each material and a new approach which utilizes information criteria and probability distributions. Nickel decreases the shear velocity of iron, while 10 at% Si has little to no effect on the shear velocity of Fe0.91Ni0.09. We observe that the shape of the phonon DOS of these alloys remains similar with increasing pressure. In the measured compression range, we therefore apply a generalized scaling law to describe the volume dependence of the phonon DOS and find that the vibrational Grüneisen parameters of hcp-Fe0.91Ni0.09 are nearly indistinguishable from those hcp-Fe and those for Fe0.8Ni0.1Si0.1 trend lower. From the vibrational free energy, we constrain the harmonic vibrational component of thermal pressure, which shows a significant positive deviation from theoretical calculations of hcp-Fe at pressures and temperatures of Earth's core. Collectively, our results demonstrate that the effects of nickel should be considered when modeling iron-rich planetary cores.},
doi = {10.1016/j.pepi.2019.05.011},
journal = {Physics of the Earth and Planetary Interiors},
number = C,
volume = 294,
place = {United States},
year = {2019},
month = {9}
}

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