| 1. |
- Bykov, M., et al.
(author)
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Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains
- 2018
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In: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Journal article (peer-reviewed)abstract
- Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N-2 in a laser-heated diamond anvil cell, we synthesize three ironnitrogen compounds Fe3N2, FeN2 and FeN4. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe3N2, synthesized at 50 GPa, is isostructural to chromium carbide Cr3C2. FeN2 has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN4, synthesized at 106 GPa, features polymeric nitrogen chains of [N-4(2-)](n) units. Based on results of structural studies and theoretical analysis, [N-4(2-)](n) units in this compound reveal catena-poly[tetraz-1-ene-1,4-diyl] anions.
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| 2. |
- Koemets, E., et al.
(author)
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Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2
- 2021
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:10
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Journal article (peer-reviewed)abstract
- Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe(2)O(3) and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mossbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory + dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites.
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| 3. |
- Serovaiskii, Aleksandr, et al.
(author)
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Fate of Hydrocarbons in Iron-Bearing Mineral Environments during Subduction
- 2019
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In: Minerals. - : MDPI. - 2075-163X. ; 9:11
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Journal article (peer-reviewed)abstract
- Subducted sediments play a key role in the evolution of the continental crust and upper mantle. As part of the deep carbon cycle, hydrocarbons are accumulated in sediments of subduction zones and could eventually be transported with the slab below the crust, thus affecting processes in the deep Earth's interior. However, the behavior of hydrocarbons during subduction is poorly understood. We experimentally investigated the chemical interaction of model hydrocarbon mixtures or natural oil with ferrous iron-bearing silicates and oxides (representing possible rock-forming materials) at pressure-temperature conditions of the Earth's lower crust and upper mantle (up to 2000(+/- 100) K and 10(+/- 0.2) GPa), and characterized the run products using Raman and Mossbauer spectroscopies and X-ray diffraction. Our results demonstrate that complex hydrocarbons are stable on their own at thermobaric conditions corresponding to depths exceeding 50 km. We also found that chemical reactions between hydrocarbons and ferrous iron-bearing rocks during slab subduction lead to the formation of iron hydride and iron carbide. Iron hydride with relatively low melting temperature may form a liquid with negative buoyancy that could transport reduced iron and hydrogen to greater depths.
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