Sound velocity of liquid Fe-Ni-S at high pressure

The sound velocity of liquid Fe47Ni28S25 and Fe63Ni12S25 was measured up to 52 GPa/2480 K in externally-resistance-heated and laser-heated diamond-anvil cells (DACs) using high-resolution inelastic X-ray scattering. From these experimental data, we obtained the elastic parameters of liquid Fe47Ni28S25, KS0 = 96.1 ± 2.7 GPa and KS0’ = 4.00 ± 0.13, where KS0 and KS0’ are the adiabatic bulk modulus and its pressure derivative at 1 bar, when the density is fixed at ρ0 = 5.62 ± 0.09 g/cm3 for 1 bar and 2000 K. With these parameters, the sound velocity and density of liquid Fe47Ni28S25 were calculated to be 8.41 ± 0.17 km/s and 8.93 ± 0.19 to 9.10 ± 0.18 g/cm3, respectively, at the core mantle boundary (CMB) conditions of 135 GPa and 3600 − 4300 K. These values are 9.4 % higher and 17–18 % lower than those of pure Fe respectively. Extrapolation of measurements and comparison with seismological models suggest the presence of 5.8–7.5 wt.% sulfur in the Earth's outer core if it is the only light element.