Sound velocity of Fe3C at high pressure and high temperature determined by inelastic X-ray scattering

The sound velocity of Fe₃C was measured at pressures from 33 to 86 GPa and at ambient and high temperatures up to 2300 K using inelastic X-ray scattering (IXS) from laser-heated samples in diamond anvil cells (DACs). The compressional velocity (V_P) and density of Fe₃C at room temperature were observed to follow a linear relationship (Birch's law). The temperature dependency of Birch's law was not clearly observed and can be ignored. Birch's law for Fe₃C is expressed by: $V_{\text{P}}=1.09\left(\pm 0.14\right)\times \rho -1.79\left(\pm 1.26\right)$. The result indicates that V_P and V_S (shear velocity) of the preliminary reference Earth model (PREM) inner core at the Inner Core Boundary (ICB) were by 12% and 48% smaller than those of Fe₃C, which could be accounted for by the premelting effect by analogy from pure Fe or by partial melting of the Fe–Fe₃C mixture in the inner core.