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Elasticity of iron at the temperature of the Earth's inner core

Steinle-Neumann, Gerd and Stixrude, Lars and Cohen, R. E. and Gülseren, Oguz (2001) Elasticity of iron at the temperature of the Earth's inner core. Nature, 413 (6851). pp. 57-60. ISSN 0028-0836. doi:10.1038/35092536.

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Seismological body-wave and free-oscillation studies of the Earth's solid inner core have revealed that compressional waves traverse the inner core faster along near-polar paths than in the equatorial plane. Studies have also documented local deviations from this first-order pattern of anisotropy on length scales ranging from 1 to 1,000 km. These observations, together with reports of the differential rotation of the inner core, have generated considerable interest in the physical state and dynamics of the inner core, and in the structure and elasticity of its main constituent, iron, at appropriate conditions of pressure and temperature. Here we report first-principles calculations of the structure and elasticity of dense hexagonal close-packed (h.c.p.) iron at high temperatures. We find that the axial ratio c/a of h.c.p. iron increases substantially with increasing temperature, reaching a value of nearly 1.7 at a temperature of 5,700 K, where aggregate bulk and shear moduli match those of the inner core. As a consequence of the increasing c/a ratio, we have found that the single-crystal longitudinal anisotropy of h.c.p. iron at high temperature has the opposite sense from that at low temperature. By combining our results with a simple model of polycrystalline texture in the inner core, in which basal planes are partially aligned with the rotation axis, we can account for seismological observations of inner-core anisotropy.

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Cohen, R. E.0000-0001-5871-2359
Additional Information:© 2001 Macmillan Magazines Ltd. Received 4 April 2001; Accepted 13 July 2001. We thank B. Buffett and B. Kiefer for discussions, and H. Krakauer and D. Singh for the use of their LAPW code. This work was supported by the US National Science Foundation (R.E.C. and L.S.) and the US Department of Energy (R.E.C.). Calculations were performed on the CRAY SV1 at the Geophysical Laboratory, supported by the US National Science Foundation and the W. M. Keck Foundation.
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Department of Energy (DOE)UNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Issue or Number:6851
Record Number:CaltechAUTHORS:20150331-084539570
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Official Citation:Elasticity of iron at the temperature of the Earth's inner core p57 Gerd Steinle-Neumann, Lars Stixrude, R. E. Cohen and Oguz Gülseren doi:10.1038/35092536
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56232
Deposited By: Ruth Sustaita
Deposited On:31 Mar 2015 16:00
Last Modified:10 Nov 2021 20:56

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