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Stable magnesium peroxide at high pressure.

Lobanov SS, Zhu Q, Holtgrewe N, Prescher C, Prakapenka VB, Oganov AR, Goncharov AF - Sci Rep (2015)

Bottom Line: However, in exoplanets oxygen may be a more abundant constituent.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.

View Article: PubMed Central - PubMed

Affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.

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 (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.

No MeSH data available.


Related in: MedlinePlus

X-ray diffraction (XRD) pattern of the A1 sample before laser heating (black line), at high temperature (red line) and quenched to 300 K (blue line).Arrows mark new peaks that appear at high temperature. A thermal shift of the MgO peaks is seen at T = 2150 K indicating a uniform heating of the sample. Miller indices correspond to the indexed tetragonal unit cell. Expected positions of I4/mcm MgO2 Bragg reflections12 are shown by red ticks. Blue bars correspond to MgO. Oxygen peaks are not resolved. The wavelength is 0.3344 Å. The inset shows the experimental assemblage of type-A runs.
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f1: X-ray diffraction (XRD) pattern of the A1 sample before laser heating (black line), at high temperature (red line) and quenched to 300 K (blue line).Arrows mark new peaks that appear at high temperature. A thermal shift of the MgO peaks is seen at T = 2150 K indicating a uniform heating of the sample. Miller indices correspond to the indexed tetragonal unit cell. Expected positions of I4/mcm MgO2 Bragg reflections12 are shown by red ticks. Blue bars correspond to MgO. Oxygen peaks are not resolved. The wavelength is 0.3344 Å. The inset shows the experimental assemblage of type-A runs.

Mentions: 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). In type-A experiments we put two 4 μm thick MgO disks in the sample cavity which was subsequently filled with liquefied oxygen (Fig. 1, inset). In type-B runs we used commercially available magnesium peroxide complex (24–28% Pa3 MgO2, 42–46% MgO, ~30% Mg) mixed with submicron Au powder serving as a laser absorber. The mixture was loaded without pressure medium.


Stable magnesium peroxide at high pressure.

Lobanov SS, Zhu Q, Holtgrewe N, Prescher C, Prakapenka VB, Oganov AR, Goncharov AF - Sci Rep (2015)

X-ray diffraction (XRD) pattern of the A1 sample before laser heating (black line), at high temperature (red line) and quenched to 300 K (blue line).Arrows mark new peaks that appear at high temperature. A thermal shift of the MgO peaks is seen at T = 2150 K indicating a uniform heating of the sample. Miller indices correspond to the indexed tetragonal unit cell. Expected positions of I4/mcm MgO2 Bragg reflections12 are shown by red ticks. Blue bars correspond to MgO. Oxygen peaks are not resolved. The wavelength is 0.3344 Å. The inset shows the experimental assemblage of type-A runs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555032&req=5

f1: X-ray diffraction (XRD) pattern of the A1 sample before laser heating (black line), at high temperature (red line) and quenched to 300 K (blue line).Arrows mark new peaks that appear at high temperature. A thermal shift of the MgO peaks is seen at T = 2150 K indicating a uniform heating of the sample. Miller indices correspond to the indexed tetragonal unit cell. Expected positions of I4/mcm MgO2 Bragg reflections12 are shown by red ticks. Blue bars correspond to MgO. Oxygen peaks are not resolved. The wavelength is 0.3344 Å. The inset shows the experimental assemblage of type-A runs.
Mentions: 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). In type-A experiments we put two 4 μm thick MgO disks in the sample cavity which was subsequently filled with liquefied oxygen (Fig. 1, inset). In type-B runs we used commercially available magnesium peroxide complex (24–28% Pa3 MgO2, 42–46% MgO, ~30% Mg) mixed with submicron Au powder serving as a laser absorber. The mixture was loaded without pressure medium.

Bottom Line: However, in exoplanets oxygen may be a more abundant constituent.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.

View Article: PubMed Central - PubMed

Affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.

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 (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.

No MeSH data available.


Related in: MedlinePlus