Shock-induced phase transitions in the MgO-FeO system to 200 GPa

We report new shock-compression data for single-crystal MgO at 114 and 192 GPa. Our data together with the existing shock-wave data revealed a volume discontinuity at 170 +/- 10 GPa along with the MgO Hugoniot. The discontinuity gives a volume increase of 1.9%, indicating a possible phase transition from a rock-salt structure (B1) to a high-temperature phase along with the MgO Hugoniot. We re-examined the Hugoniot data on polycrystalline sample (Mg-0.6, Fe-0.4)O up to 200GPa [M.S. Vassiliou, T.J. Ahrens, The equation of state of Mg0.6Fe0.4O to 200 GPa, Geophys. Res. Lett. 9 (1982) 127-130], which showed similar discontinuity with a 2.2% volume increase at 135 +/- 10 GPa. Our results add to fundamental understandings of the behavior of MgO and the lower mantle mineral magnesiowustite (Mg, Fe)O at ultrahigh pressure and temperature. (C) 2008 Elsevier Ltd. All rights reserved.