Raman spectroscopy of hcp-Fe to 152 GPa
We measured the Raman spectra of hcp-Fe from 15 to 152 GPa using the diamond anvil cell and ultrapure synthetic diamond anvils. These results were published in Science in june 2000.
The hcp phase of iron has one Raman active mode of E2g symmetry. It exhibits a sublinear frequency increase with pressure. The first figure shows our measurements (blue circles and green squares) and predictions from first-principles calculations for ambient temperature (in red).
The pressure dependence of the Raman mode can be used to
calculate the Grüneisen parameter of the raman mode,
and then approximate the thermal Grüneisen
parameter and its volume dependence. Fitting the relation
In the hcp-lattice, the E2g Raman mode and the
C44 elastic modulus are properties of the same
phonon branch. Using phenomenological modeling, they can be
These results are of great importance for understanding the high-pressure thermodynamic and elastic properties of hcp-Fe, the major constituent of the Earth's inner core. It also proves the feasability of Raman measurements on metals under extreme pressure conditions.
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