Theoretical study of γ′-Fe4N and ɛ-Fe x N iron nitrides at pressures up to 500 GPa

Попов, Захар И.; Litasov, Konstantin D.; Gavryushkin, Pavel N.; Овчинников, С. Г.; Федоров, А. С.

doi:10.1134/s0021364015060090

Cited by 16 publications

(30 citation statements)

References 27 publications

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“…Compressibility data for ε‐Fe 3 N x , γ′‐Fe 4 N, and γ‐Fe 4 N y obtained from high‐pressure experiments indicate relatively low K T 0 and K T ′ comparable with that for hcp‐Fe (Table and Figure ) [ Sakai et al , ]. Ab initio calculations indicate that ferromagnetic ε‐Fe 3 N x has higher K T of 214–226 GPa, increasing with the N‐content of the nitride [ Popov et al , ]. The magnetic transitions were not detected in present study, whereas ab initio calculations indicate that they occur at different pressure ranges for different nitride compositions.…”

Section: Discussionmentioning

confidence: 99%

“…The magnetic transitions were not detected in present study, whereas ab initio calculations indicate that they occur at different pressure ranges for different nitride compositions. A significant drop of magnetic moments occurs at 50–100 GPa and above 200 GPa all ε‐Fe 3 N x with x = 0.75–1.5 being nonmagnetic [ Popov et al , ]. Thus, at the pressures of the Earth's inner core we expect stability of nonmagnetic Fe‐nitrides, which, similarly to Fe‐carbides [ Bazhanova et al , ; Litasov et al , ; Mookherjee , ; Mookherjee et al , ], have much higher K T (295–304 GPa for ε‐Fe 3 N x ) [ Popov et al , ], relative to magnetic phases.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, thermal parameters for magnetic nitrides cannot be directly applied to nonmagnetic ones at the inner core conditions. Nevertheless, taking into account insignificant volume jump across the magnetic transitions of Fe‐nitrides [ Popov et al , ], we can suggest that thermal parameters of nonmagnetic β‐Fe 7 N 3 can be very similar to those of ε‐Fe 7 N 3 . Similar assumptions were previously applied for nonmagnetic Fe‐carbides [ Chen et al , ; Litasov et al , ].…”

Section: Discussionmentioning

confidence: 99%

“…Fe-nitrides have complex chemistry and stoichiometry at high pressure and reveal not only compositional variations but also structural and magnetic transitions [Minobe et al, 2015;Popov et al, 2015;Widenmeyer et al, 2014]. In this work we determined the thermoelastic parameters for ε-Fe 3 N 1.26 , clarified the EOS for ε-Fe 3 N 0.8 (reported in Litasov et al [2014]), and approximated parameters for ε-Fe 3 N 1.04 and γ-Fe 4 N 0.35 .…”

Section: Discussionmentioning

confidence: 99%

“…Recent diamond anvil cell experiments at 40–150 GPa revealed the stability of a new phase, β‐Fe 7 N 3 , with P 6 3 mc space group [ Minobe et al , ]. Theoretical study of elasticity and electronic structure of iron nitrides was reported in Guo et al [], Niewa et al [, ], Popov et al [], Shi et al [], and Zhang et al [].…”

Section: Introductionmentioning

confidence: 99%

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Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

et al. 2017

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Nitrogen abundance is one of the most uncertain among all elements in the Earth's interior. Recent data indicate an affinity between Fe‐nitrides and Fe‐carbides in the Earth's mantle and inner core. In this work P‐V‐T equations of state of ε‐Fe3N0.8 and ε‐Fe3N1.26 (which is close to Fe7N3) have been determined using a combination of multianvil and synchrotron radiation techniques at pressures up to 30 GPa and temperatures up to 1473 K. A fit of the P‐V‐T data to the Vinet‐Rydberg and Mie‐Grüneisen‐Debye equations of state yields the following thermoelastic parameters for the ε‐Fe3N0.8: V0 = 81.44(2) Å3, KT0 = 157(3) GPa, KT′ = 5.3 (fixed), θ0 = 555 K (fixed), γ0 = 1.83(1), and q = 1.34(18). For ε‐Fe3N1.26 we obtained V0 = 86.18(2) Å3, KT0 = 163(2) GPa, KT′ = 5.3(2), θ0 = 562(90) K, γ0 = 1.85(2), and q = 0.55(24). It is likely that all presumably paramagnetic ε‐Fe3Nx with x = 0.75–1.5 have similar thermoelastic properties with a minor increase of the bulk modulus with increasing N content. The melting temperature of ε‐Fe3Nx increases from approximately 1473 to 1573 K in the pressure range from 5 to 30 GPa. We also determined a preliminary equation of state for γ‐Fe4Ny and calculated y = 0.35(2) from the data at 20–30 GPa. Combining the results with a recent experimental study on the stability of β‐Fe7N3, isostructural with Fe7C3, and a theoretical study of the magnetic transitions in ε‐Fe3Nx, we estimate the density of Fe‐nitrides at the Earth's inner core conditions. Our results indicate that at 5000–6000 K, 2.0–3.2 wt % N can explain the density deficit in Earth's inner core.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

et al. 2017

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Non-free gas of dipoles of non-singular screw dislocations and the shear modulus near the melting

Malyshev

2014

Annals of Physics

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The behavior of the shear modulus caused by proliferation of dipoles of non-singular screw dislocations with finite-sized core is considered. The representation of twodimensional Coulomb gas with smoothed-out coupling is used, and the stress-stress correlation function is calculated. A convolution integral expressed in terms of the modified Bessel function K 0 is derived in order to obtain the shear modulus in approximation of interacting dipoles. Implications are demonstrated for the shear modulus near the melting transition which are due to the singularityless character of the dislocations.

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Composition of the Earth’s core: A review

Litasov

Shatskiy

2016

Russian Geology and Geophysics

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This paper provides the state-of-the-art discussion of major aspects of the composition and evolution of the Earth’s core. A comparison of experimentally-derived density of Fe with seismological data shows that the outer liquid core has a homogeneous structure and a ~10% density deficit, whereas the solid inner core has a complex heterogeneous anisotropic structure and a ~5% density deficit. Recent estimations of the core-mantle boundary (CMB) and inner core boundary temperatures are equal to 3800–4200 K and 5200–5700 K, respectively. Si and O (up to 5–7 wt.%) are considered to be the most likely light element candidates in the liquid core. Cosmochemical estimates show that the core must contain about 2 wt.% S and new experimental data indicate that the inner core structure gives the best match to the properties of Fe carbides. Our best estimate of the Earth’s core calls for 5–6 wt.% Si, 0.5–1.0 wt.% O, 1.8–1.9 wt.% S, and 2.0 wt.% C, with the Fe7C3 carbide being the dominant phase in the inner core. The study of short-lived isotope systems shows that the core could have formed early in the Earth’s history within about 30–50 Myr after the formation of the Solar System, t0 = 4567.2 ± 0.5 Ma. Studies on the partitioning of siderophile elements between liquid iron and silicate melt suggest that the core material would be formed in a magma ocean at ~1000–1500 km depths and 3000–4000 K. The oxygen fugacity for the magma ocean is estimated to vary from 4–5 to 1–2 log units below the Iron-Wustite oxygen buffer. However, the data for Mo, W, and S suggest addition of a late veneer of 10–15% of oxidized chondritic material as a result of the Moon-forming giant impact. Thermal and energetics core models agree with the estimate of a mean CMB heat flow of 7–17 TW. The excess heat is transported out of the core via two large low shear velocity zones at the base of superplumes. These zones may not be stable in their positions over geologic time and could move according to cycles of mantle plume and plate tectonics. The CMB heat fluxes are controlled either by high heat production from the core or subduction of cold slabs, but in both cases are closely linked with surface geodynamic processes and plate tectonic motions. Considerable amounts of exchange may have occurred between the core and mantle early in the Earth’s history even up to the formation of a basal magma ocean. However, the extent of material exchange across the CMB upon cooling of the mantle was no greater than 1–2% of the core’s mass, which, however, was sufficient to supply thermochemical plumes with volatiles H, C, and S.

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Theoretical study of γ′-Fe4N and ɛ-Fe x N iron nitrides at pressures up to 500 GPa

Cited by 16 publications

References 27 publications

Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

Non-free gas of dipoles of non-singular screw dislocations and the shear modulus near the melting

Composition of the Earth’s core: A review

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Theoretical study of γ′-Fe4N and ɛ-Fe x N iron nitrides at pressures up to 500 GPa

Cited by 16 publications

References 27 publications

Equations of state of iron nitrides ε‐Fe3Nx and γ‐Fe4Ny to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

Equations of state of iron nitrides ε‐Fe3Nx and γ‐Fe4Ny to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

Non-free gas of dipoles of non-singular screw dislocations and the shear modulus near the melting

Composition of the Earth’s core: A review

Contact Info

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Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core

Equations of state of iron nitrides ε‐Fe₃N_x and γ‐Fe₄N_y to 30 GPa and 1200 K and implication for nitrogen in the Earth's core