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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

The 300 K third-order Birch-Murnaghan EOS of I4/mcm MgO2.Red line is EOS fit to the experimental data from runs A1, A2 (red circles), and B2 (red triangles) collected upon compression. Blue line is EOS fit to the experimental data collected on decompression (B2* in the Supplementary Table S1). The pressure error bar is based on the reported uncertainty of the MgO EOS (A-runs) and the maximum pressure difference between MgO and Au pressure gauges (B-runs). Green diamonds and green line are the DFT EOS of I4/mcm phase. Black dashed line is the sum of the unit cell volumes of MgO and O2 (taken with proper coefficients as dictated by the synthesis reaction and the number of formula units in the MgO and O2 unit cells). Inset: Experimental pressure-composition phase diagram of the Mg-O system as determined in this work. Stable phases are shown with thick solid lines.
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f6: The 300 K third-order Birch-Murnaghan EOS of I4/mcm MgO2.Red line is EOS fit to the experimental data from runs A1, A2 (red circles), and B2 (red triangles) collected upon compression. Blue line is EOS fit to the experimental data collected on decompression (B2* in the Supplementary Table S1). The pressure error bar is based on the reported uncertainty of the MgO EOS (A-runs) and the maximum pressure difference between MgO and Au pressure gauges (B-runs). Green diamonds and green line are the DFT EOS of I4/mcm phase. Black dashed line is the sum of the unit cell volumes of MgO and O2 (taken with proper coefficients as dictated by the synthesis reaction and the number of formula units in the MgO and O2 unit cells). Inset: Experimental pressure-composition phase diagram of the Mg-O system as determined in this work. Stable phases are shown with thick solid lines.

Mentions: Figure 6 shows a fit of the I4/mcm MgO2 P-V data collected upon compression (red line) and decompression (blue line) to the room temperature third-order Birch-Murnaghan equation of state (EOS). Sample annealing was not performed upon decompression which resulted in less precise P-V information. We also computed the I4/mcm MgO2 volume in the 70–150 GPa pressure range (Supplementary Table S2). The EOS parameters are reported in the Supplementary Table S3. The theoretically computed volumes are systematically 1.1% larger than the experimental ones in the 100–150 GPa pressure range, which is within the computational uncertainty.


Stable magnesium peroxide at high pressure.

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

The 300 K third-order Birch-Murnaghan EOS of I4/mcm MgO2.Red line is EOS fit to the experimental data from runs A1, A2 (red circles), and B2 (red triangles) collected upon compression. Blue line is EOS fit to the experimental data collected on decompression (B2* in the Supplementary Table S1). The pressure error bar is based on the reported uncertainty of the MgO EOS (A-runs) and the maximum pressure difference between MgO and Au pressure gauges (B-runs). Green diamonds and green line are the DFT EOS of I4/mcm phase. Black dashed line is the sum of the unit cell volumes of MgO and O2 (taken with proper coefficients as dictated by the synthesis reaction and the number of formula units in the MgO and O2 unit cells). Inset: Experimental pressure-composition phase diagram of the Mg-O system as determined in this work. Stable phases are shown with thick solid lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: The 300 K third-order Birch-Murnaghan EOS of I4/mcm MgO2.Red line is EOS fit to the experimental data from runs A1, A2 (red circles), and B2 (red triangles) collected upon compression. Blue line is EOS fit to the experimental data collected on decompression (B2* in the Supplementary Table S1). The pressure error bar is based on the reported uncertainty of the MgO EOS (A-runs) and the maximum pressure difference between MgO and Au pressure gauges (B-runs). Green diamonds and green line are the DFT EOS of I4/mcm phase. Black dashed line is the sum of the unit cell volumes of MgO and O2 (taken with proper coefficients as dictated by the synthesis reaction and the number of formula units in the MgO and O2 unit cells). Inset: Experimental pressure-composition phase diagram of the Mg-O system as determined in this work. Stable phases are shown with thick solid lines.
Mentions: Figure 6 shows a fit of the I4/mcm MgO2 P-V data collected upon compression (red line) and decompression (blue line) to the room temperature third-order Birch-Murnaghan equation of state (EOS). Sample annealing was not performed upon decompression which resulted in less precise P-V information. We also computed the I4/mcm MgO2 volume in the 70–150 GPa pressure range (Supplementary Table S2). The EOS parameters are reported in the Supplementary Table S3. The theoretically computed volumes are systematically 1.1% larger than the experimental ones in the 100–150 GPa pressure range, which is within the computational uncertainty.

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