Stable magnesium peroxide at high pressure.

Sergey S Lobanov,Nicholas Holtgrewe,Clemens Prescher,Qiang Zhu,Artem R Oganov,Alexander F Goncharov,Vitali B Prakapenka

doi:10.1038/srep13582

Abstract

Rocky planets are thought to comprise compounds of Mg and O as these are among the most abundant elements, but knowledge of their stable phases may be incomplete. MgO is known to be remarkably stable to very high pressure and chemically inert under reduced condition of the Earth’s lower mantle. However, in exoplanets oxygen may be a more abundant constituent. Here, using synchrotron x-ray diffraction in laser-heated diamond anvil cells, we show that MgO and oxygen react at pressures above 96 GPa and T = 2150 K with the formation of I4/mcm MgO2. Raman spectroscopy detects the presence of a peroxide ion (O22−) in the synthesized material as well as in the recovered specimen. Likewise, energy-dispersive x-ray spectroscopy confirms that the recovered sample has higher oxygen content than pure MgO. Our finding suggests that MgO2 may be present together or instead of MgO in rocky mantles and rocky planetary cores under highly oxidized conditions.

Highlights

We report on the synthesis of I4/mcm MgO2 in a laser-heated diamond anvil cell (DAC)
Our finding suggests that the Mg-Fe-Si-O system likely has more unexpected chemistry at high pressure
Two types of chemical precursors were loaded in DACs to study the MgO-O2 phase diagram in the 0–160 GPa pressure range

Summary

Introduction

We report on the synthesis of I4/mcm MgO2 in a laser-heated diamond anvil cell (DAC). Two types of chemical precursors were loaded in DACs to study the MgO-O2 phase diagram in the 0–160 GPa pressure range (see Table 1 and Methods).

Results

Conclusion