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Science 2 June 2000:
Vol. 288. no. 5471, pp. 1626 - 1629
DOI: 10.1126/science.288.5471.1626
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Reports

Raman Spectroscopy of Iron to 152 Gigapascals: Implications for Earth's Inner Core

Sébastien Merkel, 12 Alexander F. Goncharov, 1 Ho-kwang Mao, 1 Philippe Gillet, 2 Russell J. Hemley 1

Raman spectra of hexagonal close-packed iron (epsilon -Fe) have been measured from 15 to 152 gigapascals by using diamond-anvil cells with ultrapure synthetic diamond anvils. The results give a Grüneisen parameter gamma 0 = 1.68 (±0.20) and q = 0.7 (±0.5). Phenomenological modeling shows that the Raman-active mode can be approximately correlated with an acoustic phonon and thus provides direct information about the high-pressure elastic properties of iron, which have been controversial. In particular, the C44 elastic modulus is found to be lower than previous determinations. This leads to changes of about 35% at core pressures for shear wave anisotropies.

1 Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA.
2 Laboratoire des Sciences de la Terre, UMR CNRS 5570, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France.

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