Phonon density of states of iron up to 153 gigapascals

We report phonon densities of states (DOS) of iron measured by nuclear reso nant inelastic x-ray scattering to 153 gigapascals and calculated from ab i nitio theory. Qualitatively, they are in agreement, but the theory predicts density at higher energies. From the DOS, we derive elastic and thermodyna mic parameters of iron, including shear modulus, compressional and shear ve locities, heat capacity, entropy, kinetic energy, zero-point energy, and De bye temperature. In comparison to the compressional and shear velocities fr om the preliminary reference Earth model (PREM) seismic model, our results suggest that Earth's inner core has a mean atomic number equal to or higher than pure iron, which is consistent with an iron-nickel alloy.