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Updated: Jul 11, 2026

Ultrasound Velocity Measurement in a Liquid Metal Electrode
Published on: August 5, 2015
Sound velocities in iron to 110 gigapascals
1Laboratoire de Minéralogie et Cristallographie, UMR CNRS 7590, Université Paris VI, 4 Place Jussieu, 75252 Paris cedex 06, France. fiquet@lmcp.jussieu.fr
Abstract:
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.
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