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

Morrison, Rachel A. and Jackson, Jennifer M. and Sturhahn, Wolfgang and Zhao, Jiyong and Toellner, Thomas S. (2019) High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys. Physics of the Earth and Planetary Interiors, 294 . Art. No. 106268. ISSN 0031-9201.

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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_(0.91)Ni_(0.09) and Fe_(0.8)Ni_(0.1)Si_(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_(0.91)Ni_(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 therefore apply a generalized scaling law to describe the volume dependence of the phonon DOS and find that the vibrational Grüneisen parameters of hcp-Fe_(0.91)Ni_(0.09) are nearly indistinguishable from those hcp-Fe and those for Fe_(0.8)Ni_(0.1)Si_(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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Morrison, Rachel A.0000-0003-3585-827X
Jackson, Jennifer M.0000-0002-8256-6336
Sturhahn, Wolfgang0000-0002-9606-4740
Zhao, Jiyong0000-0002-0777-3626
Additional Information:© 2019 Published by Elsevier B.V. Received 31 October 2018, Revised 28 April 2019, Accepted 10 May 2019, Available online 29 May 2019. We thank Lisa Mauger and Caitlin Murphy for help with sample synthesis, Dongzhou Zhang and Caitlin Murphy for help during the NRIXS and XRD experiments, and Muir Morrison for helpful discussion of the sound velocity analysis. We thank NSF-EAR-1727020, W.M. Keck Institute for Space Studies, and NDSEG for support of this work. Sector 3 operations, GSECARS sector 13-BM-C, and the gas loading facility are partially supported by COMPRES. Use of APS is supported by the U.S. DOE, Office of Science (DE-AC02-06CH11357). Microprobe analyses were carried out at the Caltech GPS Division Analytical Facility (funded in part by the MRSEC Program of the NSF under DMR-0080065). The data used are listed in the tables, supporting information, and references. The authors have no competing interests to declare.
Group:Keck Institute for Space Studies, Seismological Laboratory
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
Department of Energy (DOE)DE-AC02-06CH11357
Subject Keywords:Earth's core; Sound velocity; Grüneisen parameter; High pressure; Nuclear resonant inelastic X-ray spectroscopy
Record Number:CaltechAUTHORS:20190529-153502145
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Official Citation:Rachel A. Morrison, Jennifer M. Jackson, Wolfgang Sturhahn, Jiyong Zhao, Thomas S. Toellner, High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys, Physics of the Earth and Planetary Interiors, Volume 294, 2019, 106268, ISSN 0031-9201, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95890
Deposited By: Tony Diaz
Deposited On:29 May 2019 22:47
Last Modified:13 Aug 2019 18:05

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