Phase Relations of Iron Carbides Fe2C, Fe3C, and Fe7C3 at the Earth’s Core Pressures and Temperatures

Sagatov, Nursultan E.; Gavryushkin, Pavel N.; Medrish, I. V.; Inerbaev, Talgat M.; Litasov, Konstantin D.

doi:10.15372/rgg2019146

Cited by 6 publications

(9 citation statements)

References 46 publications

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“…All structures are dynamically stable, which was confirmed using the calculated phonon spectra (Figure ). Fe 3 N- C 2/ m is isostructural to Fe 3 C- C 2/ m -II . In this structure, nitrogen atoms are bonded to 7 Fe atoms, forming [FeN 7 ] one-capped trigonal prisms connected with each other by edges and faces (Figure a).…”

Section: Resultsmentioning

confidence: 99%

Fe–N System at High Pressures and Its Relevance to the Earth’s Core Composition

Sagatov

Sagatova

Gavryushkin

et al. 2021

Crystal Growth & Design

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Based on ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of iron−nitrogen compounds in the pressure range of 100−400 GPa and temperatures up to 4000 K were determined. Three new iron nitrides Fe 4 N 3 -Imm2, Fe 2 N-Pnma, and Fe 3 N-C2/m were predicted. Fe 4 N 3 was shown to be stable at pressures up to 266 GPa and then decompose into Fe 2 N + 2FeN. Predicted Fe 2 N-Pnma becomes stable with respect to the decomposition reaction 9Fe 2 N = Fe 4 N 3 + 2Fe 7 N 3 at pressures above 221 GPa. Fe 3 N-C2/m stabilizes with respect to decomposition into 2Fe + Fe 7 N 3 at pressures above 265 GPa. Also, it was shown that β-Fe 7 N 3 synthesized in diamond anvil cell experiments has an orthorhombic Pbca structure, and at pressures above ∼320 GPa decomposes into 2Fe 2 N + Fe 3 N. All predicted Fe-rich iron nitrides, except Fe 4 N 3 -Imm2, have structural analogs among iron carbides. Considering the temperature effect, we observed that FeN-P2 1 3, Fe 2 N-Pnma, and Fe 3 N-C2/m can be stable at the Earth's inner core pressures and temperatures up to 4000 K, whereas Fe 4 N 3 -Imm2 and β-Fe 7 N 3 are thermodynamically unstable in the entire studied temperature range. Although Fe 7 N 3 -Pbca is thermodynamically unstable at inner core pressures, it shows the closest coincidence of the S-and P-wave velocities with seismic observations among the studied Fe-nitrides. Overall, Fe-nitrides cannot be the major compounds in the inner core of the Earth and can only substitute other elements such as carbon in Fe-carbides in minor amounts.

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Section: Resultsmentioning

confidence: 99%

Fe–N System at High Pressures and Its Relevance to the Earth’s Core Composition

Sagatov

Sagatova

Gavryushkin

et al. 2021

Crystal Growth & Design

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“…On the other hand, a recent theoretical study has predicted a new monoclinic high‐ P phase for Fe 7 N 3 and Fe 7 C 3 above ∼250 GPa (Sagatov et al., 2019). Subsequent simulations suggested that Fe 7 C 3 might decompose into the mixture of Fe 2 C and Fe 3 C at conditions of the Earth's inner core (Sagatov et al., 2020). Whether these results could be applied in the Fe‐N‐C ternary system is still under debate.…”

Section: Discussionmentioning

confidence: 99%

High‐Pressure Phase Stability and Thermoelastic Properties of Iron Carbonitrides and Nitrogen in the Deep Earth

Huang

Zhu

et al. 2021

JGR Solid Earth

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Nitrogen (N) is one of the most significant volatiles in our planet, an essential element for life, and the primary component of the atmosphere. Nitrogen in the Earth's interior is linked to that near the surface through processes of subduction and volcanic outgassing, influencing the partial pressure (P) of atmospheric N in a profound way (Busigny et al., 2019;Mikhail & Sverjensky, 2014). This "deep nitrogen" also provides crucial insights into planetary evolution, including the accretion and differentiation of the core and mantle

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“…In this case, the cutoff energy was increased to 1000 eV. The calculation of the Gibbs free energy dependence on temperature was performed according to the methodology described in our previous work. , …”

Section: Methodsmentioning

confidence: 99%

Experimental and Ab Initio Investigation of the Formation of Phosphoran Olivine

Bekker

Litasov

Shatskiy

et al. 2021

ACS Earth Space Chem.

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With the use of both experimental and numerical methods, the conditions required for phosphoran olivine formation as well as its structural features and thermodynamic stability have been studied. Olivine containing up to 35 wt % P 2 O 5 was synthesized in evacuated quartz glass ampoules at temperatures of 1373, 1473, and 1573 K using San Carlos olivine or an oxide mixture blended with either magnesium phosphate Mg 3 (PO 4 ) 2 or iron phosphide FeP and studied by scanning electron microscopy/ energy-dispersive spectrometry, wavelength-dispersive spectroscopy analysis, X-ray powder diffraction, and Raman spectroscopy. The inhomogeneity of the composition of synthesized phosphoran olivines as well as the results of first-principles calculations unequivocally indicates their metastable crystallization. The absence of the shift of phosphoran olivine X-ray diffraction reflections with respect to phosphoran-free olivine might indicate that the entry of phosphorus in olivine causes only a slight distortion of the structure, which is consistent with the results of first-principles calculations. The position of the Raman bands associated with the most intensive internal vibration modes of [SiO 4 ] 4− tetrahedra at 824 and 857 cm −1 and [PO 4 ] 3− tetrahedra at 981 cm −1 does not change with respect to phosphoran-free olivine and farringtonite, respectively. Their relative intensities in phosphoran olivine may reflect the Si/P ratio. The phosphoran olivine formation energy is dependent on the distance between [PO 4 ] 3− tetrahedra in the structure. With the use of first-principles calculations, it has been shown that neither pressure in the range from 0 to 8 GPa nor temperature in the range from 0 to 1500 K favors the equilibrium entry of phosphorus into olivine at concentrations equal to or exceeding 6.3 wt %.

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Phase Relations of Iron Carbides Fe2C, Fe3C, and Fe7C3 at the Earth’s Core Pressures and Temperatures

Cited by 6 publications

References 46 publications

Fe–N System at High Pressures and Its Relevance to the Earth’s Core Composition

Fe–N System at High Pressures and Its Relevance to the Earth’s Core Composition

High‐Pressure Phase Stability and Thermoelastic Properties of Iron Carbonitrides and Nitrogen in the Deep Earth

Experimental and Ab Initio Investigation of the Formation of Phosphoran Olivine

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