Structure and Properties of New High-Pressure Phases of Fe7N3

Gavryushkin, Pavel N.; Sagatov, Nursultan E.; Попов, Захар И.; Bekhtenova, Altyna; Inerbaev, Talgat M.; Litasov, Konstantin D.

doi:10.1134/s0021364018060061

Cited by 5 publications

(8 citation statements)

References 27 publications

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“…As mentioned earlier, nitrogen goes into interstitial sites in ε-Fe3Nx structure and therefore the configurational entropy should be larger than for γʹ-Fe4N where nitrogen substitutes for iron. A recent computational study revealed the structure of β-Fe7N3 which is characterised by the absence of a close-packed arrangement of iron unlike ε-Fe3Nx and γʹ-Fe4N (Gavryushkin et al, 2018). This may also explain the high entropy of β-Fe7N3.…”

Section: Subsolidus Phase Relations Of the System Fe-nmentioning

confidence: 99%

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Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

Breton

Komabayashi

Thompson

et al. 2019

American Mineralogist

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Compression and decompression experiments on face-centered cubic (fcc) γ′-Fe4N to 77 GPa at room temperature were conducted in a diamond-anvil cell with in situ X-ray diffraction (XRD) to examine its stability under high pressure. In the investigated pressure range, γ′-Fe4N did not show any structural transitions. However, a peak broadening was observed in the XRD patterns above 60 GPa. The obtained pressure-volume data to 60 GPa were fitted to the third-order Birch-Murnaghan equation of state (EoS), which yielded the following elastic parameters: K0 = 169 (6) GPa, K′ = 4.1 (4), with a fixed V0 = 54.95 Å at 1 bar. A quantitative Schreinemakers' web was obtained at 15–60 GPa and 300–1600 K by combining the EoS for γ′-Fe4N with reported phase stability data at low pressures. The web indicates the existence of an invariant point at 41 GPa and 1000 K where γ′-Fe4N, hexagonal closed-packed (hcp) ε-Fe7N3, double hexagonal closed-packed β-Fe7N3, and hcp Fe phases are stable. From the invariant point, a reaction γ′-Fe4N = β-Fe7N3 + hcp Fe originates toward the high-pressure side, which determines the high-pressure stability of γ′-Fe4N at 56 GPa and 300 K. Therefore, the γ′-Fe4N phase observed in the experiments beyond this pressure must be metastable. The obtained results support the existing idea that β-Fe7N3 would be the most nitrogen-rich iron compound under core conditions. An iron carbonitride Fe7(C,N)3 found as a mantle-derived diamond inclusion implies that β-Fe7N3 and Fe7C3 may form a continuous solid solution in the mantle deeper than 1000 km depth. Diamond formation may be related to the presence of fluids in the mantle, and dehydration reactions of high-pressure hydrous phase D might have supplied free fluids in the mantle at depths greater than 1000 km. As such, the existence of Fe7(C,N)3 in diamond can be an indicator of water transportation to the deep mantle.

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Section: Subsolidus Phase Relations Of the System Fe-nmentioning

confidence: 99%

“…Recently Gavryushkin et al (2018) predicted a new form of Fe7N3 which take an orthorhombic structure with the space group of Amm2. Amm2-Fe7N3 may be stable between ε-Fe7N3 and β-Fe7N3 at 0K.…”

Section: Subsolidus Phase Relations Of the System Fe-nmentioning

confidence: 99%

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

Breton

Komabayashi

Thompson

et al. 2019

American Mineralogist

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“…However, based on the similarity of its powder diffraction pattern to that of h-Fe 7 C 3 , the conclusion about similarity of their structures has been inferred. With DFT calculations we have conrmed this conclusion, shown that b-Fe 7 N 3 (isostructural to h-Fe 7 C 3 ) became more favourable than 3phase at pressures above 67 GPa at 0 K. 23 In the same work we also found the new phase Fe 7 N 3 -Amm2, which is energetically more favourable than the b-phase in the pressure range of 43-128 GPa at 0 K. The apparent difference between the experimental and theoretical stability elds of the band Amm2-phases was explained by the kinetic effects, preventing transformation of high-temperature b-phase to the lowtemperature Amm2-phase.…”

Section: Introductionmentioning

confidence: 64%

“…Both methods show their effectiveness in predicting crystal structures of inorganic compounds, [30][31][32][33] including carbides and nitrides. 20,23,34 The calculations of the electronic structure were carried out within the DFT using the VASP 5.3 package. [35][36][37] The exchangecorrelation interaction was taken into account in the generalized gradient approximation (GGA) in the form of the Perdew-Burke-Ernzerhof (PAW) functional.…”

Section: Computational Detailsmentioning

confidence: 99%

“…[35][36][37] The exchangecorrelation interaction was taken into account in the generalized gradient approximation (GGA) in the form of the Perdew-Burke-Ernzerhof (PAW) functional. 38 Since the recent theoretical 16,18,23 and experimental 12,15 results showed that for iron carbides and nitrides, the disappearance of the magnetic moment occurs at pressures below 100 GPa, we performed non spin-polarized calculations above this pressure.…”

Section: Computational Detailsmentioning

confidence: 99%

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New high-pressure phases of Fe₇N₃ and Fe₇C₃ stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

et al. 2019

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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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Structure and Properties of New High-Pressure Phases of Fe7N3

Cited by 5 publications

References 27 publications

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

New high-pressure phases of Fe₇N₃ and Fe₇C₃ stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

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

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Structure and Properties of New High-Pressure Phases of Fe7N3

Cited by 5 publications

References 27 publications

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

New high-pressure phases of Fe7N3 and Fe7C3 stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

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

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New high-pressure phases of Fe₇N₃ and Fe₇C₃ stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds