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 86GPa and at ambient and high temperatures up to 2300K using inelastic X-ray scattering (IXS) from laser-heated samples in diamond anvil cells (DACs). The compressional velocity (VP) 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: VP=1.09±0.14×ρ−1.79±1.26. The result indicates that VP and VS (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.