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Science 4 May 2001:
Vol. 292. no. 5518, pp. 914 - 916
DOI: 10.1126/science.1057670
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Reports

Phonon Density of States of Iron up to 153 Gigapascals

H. K. Mao,1 J. Xu,1 V. V. Struzhkin,1 J. Shu,1 R. J. Hemley,1 W. Sturhahn,2 M. Y. Hu,2 E. E. Alp,2 L. Vocadlo,3 D. Alfè,3 G. D. Price,3 M. J. Gillan,3 M. Schwoerer-Böhning,4 D. Häusermann,4 P. Eng,5 G. Shen,5 H. Giefers,6 R. Lübbers,6 G. Wortmann6

We report phonon densities of states (DOS) of iron measured by nuclear resonant inelastic x-ray scattering to 153 gigapascals and calculated from ab initio theory. Qualitatively, they are in agreement, but the theory predicts density at higher energies. From the DOS, we derive elastic and thermodynamic parameters of iron, including shear modulus, compressional and shear velocities, heat capacity, entropy, kinetic energy, zero-point energy, and Debye temperature. In comparison to the compressional and shear velocities from the preliminary reference Earth model (PREM) seismic model, our results suggest that Earth's inner core has a mean atomic number equal to or higher than pure iron, which is consistent with an iron-nickel alloy.

1 Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, Washington, DC 20015, USA.
2 Advanced Photon Source, Argonne, IL 60439, USA.
3 University College London, Gower Street, London WC1E 6BT, UK.
4 High Pressure Collaborative Access Team (HPCAT), Advanced Photon Source, Argonne, IL 60439, USA.
5 Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637.
6 Fachbereich Physik, University of Paderborn, D33095 Paderborn, Germany.

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