Experimental vibrational Gruneisen ratio values for ε-iron up to 330 GPa at 300 K

Experimental values for the vibrational Gruneisen ratio, gamma (nu), for hexagonal close-packed (hcp) iron, called epsilon (epsilon)-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. Xray structural refinement using the Rietveld method on powder diffraction data yielded information on mean square displacement used to obtain the Debye temperature, theta, as a function of compression, V/V-0. The value of theta was determined from the measured intensity of the diffraction lines, which arises from the mean squared amplitude < (2) > measured in-situ in the diamond cell. From the Debye relationship, gamma (nu) = - (partial derivative In theta/partial derivative ln V)(T), we determined experimental data on gamma (nu) versus V of Fe (hcp) up to 330 GPa at 300 K. The measured value of gamma (nu)(V) is 1.18 at 330 GPa and 1.41 at 135 GPa.