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Science 19 January 2001:
Vol. 291. no. 5503, pp. 468 - 471
DOI: 10.1126/science.291.5503.468
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Reports

Sound Velocities in Iron to 110 Gigapascals

Guillaume Fiquet,1* James Badro,1 François Guyot,1 Herwig Requardt,2 Michael Krisch2

The dispersion of longitudinal acoustic phonons was measured by inelastic x-ray scattering in the hexagonal closed-packed (hcp) structure of iron from 19 to 110 gigapascals. Phonon dispersion curves were recorded on polycrystalline iron compressed in a diamond anvil cell, revealing an increase of the longitudinal wave velocity (VP) from 7000 to 8800 meters per second. We show that hcp iron follows a Birch law for VP, which is used to extrapolate velocities to inner core conditions. Extrapolated longitudinal acoustic wave velocities compared with seismic data suggest an inner core that is 4 to 5% lighter than hcp iron.

1 Laboratoire de Minéralogie et Cristallographie, UMR CNRS 7590, Université Paris VI, 4 Place Jussieu, 75252 Paris cedex 06, France.
2 European Synchrotron Radiation Facility, BP220, 38043 Grenoble cedex, France.
*   To whom correspondence should be addressed. E-mail: fiquet{at}lmcp.jussieu.fr

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