Equation of State for Fe-9.0 wt% O up to 246 GPa: Implications for Oxygen in the Earth's Outer Core

摘要

To constrain the amount of oxygen in Earth's outer core, the equation of sate (EoS) for Fe-9 wt% O (Fe-9O) was measured up to similar to 246 GPa using the dynamic compression technique. The shock velocity (U-s) and particle velocity (u(p)) relationship can be described by U-s = 4.07(21) + 1.62(7)u(p). Using the ideal mixing model, the isothermal equation of state for Fe-9O at 300 K was fitted to the third-order Birch-Murnaghan EoS with bulk modulus K-0' = 163.6(17) GPa and its pressure derivative K-0 = 4.11(6). Based on the EoS of Mie-Gruneisen, the calculated adiabat coincides with our experimental data when its Gruneisen parameters are given by gamma(0) = 2.3, q = 0.3. Using the determined parameters, bulk sound velocities were obtained from the Hugoniot data. By comparing the pressure-density profiles and sound velocities of Fe-O system with the preliminary reference Earth model, it was determined that the oxygen-rich composition does not provide a good match to the observations in the Earth's outer core.