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Grüneisen parameter of hcp‐Fe to 171 GPa

Murphy, Caitlin A. and Jackson, Jennifer M. and Sturhahn, Wolfgang and Chen, Bin (2011) Grüneisen parameter of hcp‐Fe to 171 GPa. Geophysical Research Letters, 38 . Art. No. L24306. ISSN 0094-8276.

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We measured the phonon density of states (DOS) of hexagonal close-packed iron (ɛ-Fe) with high statistical quality using nuclear resonant inelastic X-ray scattering and in situ X-ray diffraction experiments between pressures of 30 GPa and 171 GPa and at 300 K, with a neon pressure medium up to 69 GPa. The shape of the phonon DOS remained similar at all compression points, while the maximum (cutoff) energy increased regularly with decreasing volume. As a result, we present a generalized scaling law to describe the volume dependence of ɛ-Fe's total phonon DOS which, in turn, is directly related to the ambient temperature vibrational Grüneisen parameter (γ_(vib)). Fitting our individual γ_(vib) data points with γ_(vib) = γ_(vib),0(V/V0)^q, a common parameterization, we found an ambient pressure γ_(vib,0) = 2.0 ± 0.1 for the range q = 0.8 to 1.2. We also determined the Debye sound velocity (v_D) from the low-energy region of the phonon DOS and our in situ measured volumes, and used the volume dependence of v_D to determine the commonly discussed Debye Grüneisen parameter (γ_D). Comparing our γ_(vib)(V) and γ_D(V), we found γ_(vib) to be ∼10% larger than γ_D at any given volume. Finally, applying our γ_(vib)(V) to a Mie-Grüneisen type relationship and an approximate form of the empirical Lindemann melting criterion, we predict the vibrational thermal pressure and estimate the high-pressure melting behavior of ɛ-Fe at Earth's core pressures.

Item Type:Article
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URLURL TypeDescription
Jackson, Jennifer M.0000-0002-8256-6336
Sturhahn, Wolfgang0000-0002-9606-4740
Additional Information:© 2011 by the American Geophysical Union. Received 2 September 2011; revised 3 November 2011; accepted 6 November 2011; published 20 December 2011. We would like to thank D. Zhang, H. Yavas, and J.K. Wicks for assistance during the experiments, and NSF‐CAREER‐0956166 and Caltech for support of this research. We thank two anonymous reviewers for their comments that helped to improve our manuscript. Use of the Advanced Photon Source was supported by the U.S.D.O.E.,O.S.,O.B.E.S. (DE‐AC02‐06CH11357). Sector 3 operations and the GSE‐CARS gasloading facility are supported in part by COMPRES (NSF EAR 06‐49658). The Editor thanks two anonymous reviewers for their assistance in evaluating this paper.
Funding AgencyGrant Number
Department of Energy (DOE) Office of Basic EnergyDE‐AC02‐06CH11357
Record Number:CaltechAUTHORS:20120127-080434255
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Official Citation:Murphy, C. A., J. M. Jackson, W. Sturhahn, and B. Chen (2011), Grüneisen parameter of hcp-Fe to 171 GPa, Geophys. Res. Lett., 38, L24306, doi:10.1029/2011GL049531.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28990
Deposited By: Ruth Sustaita
Deposited On:30 Jan 2012 16:18
Last Modified:24 Jan 2020 17:57

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