Lobanov Sergey S, Zhu Qiang, Holtgrewe Nicholas, Prescher Clemens, Prakapenka Vitali B, Oganov Artem R, Goncharov Alexander F
Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia.
Sci Rep. 2015 Sep 1;5:13582. doi: 10.1038/srep13582.
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 (O2(2-)) 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.
岩石行星被认为由镁和氧的化合物组成，因为这些是最丰富的元素之一，但它们稳定相的知识可能并不完整。氧化镁在地球下地幔的还原条件下对非常高的压力具有显著的稳定性且化学惰性。然而，在系外行星中，氧可能是更丰富的成分。在这里，我们使用激光加热金刚石对顶砧中的同步加速器X射线衍射表明，氧化镁和氧在压力高于96吉帕和温度为2150K时发生反应，形成I4/mcm MgO₂。拉曼光谱检测到合成材料以及回收样品中存在过氧离子（O₂²⁻）。同样，能量色散X射线光谱证实回收的样品比纯氧化镁具有更高的氧含量。我们的发现表明，在高度氧化的条件下，MgO₂可能与氧化镁一起存在于岩石地幔和岩石行星核心中，或者替代氧化镁。
