Shock Compression and Phase Transitions of Magnesiowüstite (Mg,Fe)O up to Earth’s Lowermost Mantle Conditions

We report new shock-compression data for polycrystalline (Mg,Fe)O up to 130GPa shock pressures corresponding to Earth’s lowermost mantle conditions. Our data together with the existing shock-wave data of (Mg,Fe)O and its end-members MgO and FeO reveal that the Hugoniot curves of (Mg,Fe)O does not change with varying FeO content for their B1 phase (NaCl-structure) in the pressure--relative-volume plane. The evidence of the volume change within 3% at around 120GPa along the Hugoniot of (Mg_0.6, Fe_0.4)O is consistent with a structural transition from B1 phase (NaCl cubic) to B8 phase (NiAs-type hexagonal). Such a structural transition of (Mg,Fe)O, if indeed occurs, may in part contribute to the scattering of seismic waves and change in velocity gradient found in the lowermost mantle.