Synchrotron X-ray and Acoustic Studies of bcc-hcp Phase Transition of Fe

Introduction Elastic properties of hcp iron (Fe) provide crucial information about the composition and anisotropy of the Earth’s core. Recently, the phonon densities of state of hcp Fe at high pressure have been investigated up to 42 and 153 GPa by using inelastic nuclear resonance x-ray scattering. The results showed discrepancies from previous results of first-principle calculations [1, 2]. The lattice strain method [3], based on measurements of stress-induced strain along various orientations, yielded information about the elastic constants of hcp Fe to pressures of >220 GPa [4]. However, some studies argue that this method requires some assumed values in the parameterization, which result in large uncertainties in the derived elastic properties [5]. Recent results on the sound velocity of Fe from using inelastic x-ray scattering [6] support previous ultrasonic velocity measurements at ~17 GPa and results from radial x-ray diffraction [4]. In this study, we measured the elastic property of hcp Fe up to 17 GPa. These data will provide critical anchor points for those ultrahigh-pressure studies as well as for theoretical calculations.