Experimental vibrational Grüneisen ratio values for ϵ‐iron up to 330 GPa at 300 K

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Abstract
Experimental values for the vibrational Grüneisen ratio, γυ, for hexagonal close‐packed (hcp) iron, called epsilon (ϵ)‐iron, were obtained over a large compression range corresponding to Earth's inner‐core pressure. This was done by measuring the intensity change in x‐ray diffraction lines under pressure, P. X‐ray structural refinement using the Rietveld method on powder diffraction data yielded information on mean square displacement used to obtain the Debye temperature, Θ, as a function of compression, V/V0. The value of Θ was determined from the measured intensity of the diffraction lines, which arises from the mean squared amplitude < u² > measured in‐situ in the diamond cell. From the Debye relationship, γυ=−(∂ ln Θ/∂ ln V)T, we determined experimental data on γυ versus V of Fe (hcp) up to 330 GPa at 300 K. The measured value of γυ(V) is 1.18 at 330 GPa and 1.41 at 135 GPa.

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