Sound velocity measurement by inelastic X-ray scattering at high pressure and temperature by resistive heating diamond anvil cell

We determined the compressional velocity of hcp-Fe in a wide pressure and temperature range using high-resolution inelastic X-ray scattering (IXS) combined with in situ X-ray powder diffraction (XRD) on samples in resistively heated diamond anvil cells: our measurements extend up to 174GPa at room temperature, to 88GPa at 700K, and to 62.5GPa at 1000K. Our data obtained at room temperature and high temperature are well described by a linear relation to density, extending the range of verification of Birch’s law beyond previous work and suggesting only a small temperature dependence up to 1000K. When we compare the present results with the preliminary reference Earth model (PREM), we can conclude that there is either a strong temperature effect on Birch’s law at temperatures above 1000K, or the composition of the core is rather different from that commonly expected, i.e., containing heavy elements.