Stability of B2‐type FeS at Earth's inner core pressures

Gavryushkin, Pavel N.; Попов, Захар И.; Litasov, Konstantin D.; Belonoshko, Anatoly B.; Gavryushkin, Alex

doi:10.1002/2016gl069374

Cited by 10 publications

(7 citation statements)

References 37 publications

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“…For the Fe-S alloys, we deployed simulations with 9-36 sulfur atoms in the 180-atom cells (corresponding to cS=0.05~0.20, which is within the stability regime of hcp-structured Fe-S solid solutions according to previous studies (Cote et al, 2008;Gavryushkin et al, 2016)) and for each concentration we calculated its free energies through the thermodynamic integration techniques at several T-P conditions (as listed in Table 3), based on which the free energies over the pressures can be derived through the auxiliary Birch-Murnaghan equation of states at various temperatures, as listed in Appendix C.…”

Section: Free Energies Of Fe-s Alloysmentioning

confidence: 99%

Partitioning of sulfur between solid and liquid iron under Earth’s core conditions: Constraints from atomistic simulations with machine learning potentials

Zhang

Csänyi

2020

Geochimica et Cosmochimica Acta

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Partition coefficients of light elements between the solid and liquid iron phases are crucial for uncovering the state and dynamics of the Earth's core. As one of the major light element candidates, sulfur has attracted extensive interests for measuring its partitioning and phase behaviors over the last several decades, but the relevant experimental data under Earth's core conditions are still scarce. In this study, using a toolkit consisting of electronic structure theory, high-accuracy machine learning potentials and rigorous free energy calculations, we establish an efficient and extendible framework for predicting complex phase behaviors of iron alloys under extreme conditions. As a first application of this framework, we predict the partition coefficients of sulfur over wide range of temperatures and pressures (from 4000 K, 150 GPa to 6000 K, 330 GPa), which are demonstrated to be in good agreement with previous experiments and ab initio simulations. After a continuous increase below ~250 GPa, the partition coefficient is found to be around 0.750.07 at higher pressures and are essentially temperature-independent. Given these predictions, the partitioning of sulfur is confirmed to be insufficient to account for the observed density jump across the Earth's inner core boundary and its roles on the geodynamics of the Earth's core should be minor.

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Section: Free Energies Of Fe-s Alloysmentioning

confidence: 99%

Partitioning of sulfur between solid and liquid iron under Earth’s core conditions: Constraints from atomistic simulations with machine learning potentials

Zhang

Csänyi

2020

Geochimica et Cosmochimica Acta

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“…metals and light elements is unusual, at pressures where typical nonmetals like sulfur adopt metallic properties, 47 this kind of isomorphism instead becomes widespread. 39,48 The low-pressure phase Ni 3 S-I4̅ could not be characterized by a close packing as previous phases. This phase is isostructural to Ni 3 P-I4̅ (schreibersite-structured) and characterized by ninefold coordination of S by Ni, forming a muffinlike polyhedron (Figure 4e).…”

Section: ■ Results and Discussionmentioning

confidence: 81%

“…Thus, predicted Ni–S structures could be considered as ordered representatives of solid solutions. Although at ambient pressure the isomorphism between d -metals and light elements is unusual, at high pressures where typical nonmetals like sulfur adopt metallic properties, this kind of isomorphism instead becomes widespread. , Ni 14 S, Ni 13 S, and Ni 12 S are characterized by an almost ideal fcc structure, with the Ni–Ni and Ni–S distances varying in the range 2.10–2.13 Å at 300 GPa (Figure a). For comparison, the Ni–Ni distances in the structure of pure Ni are equal to 2.12 Å.…”

Section: Resultsmentioning

confidence: 99%

“…The fcc lattices containing 18, 22, 30, 32, and 72 atoms were considered for Ni. In the case of Fe, the sulfur content above ∼30 mol % stabilizes the bcc lattice relative to hcp according to the recent theoretical data. , Therefore, we considered hcp lattices containing 16, 32, 54, 72, and 128 atoms for Fe. Ni/Fe and S atoms were randomly distributed in the periodically repeated supercell using a random number generator.…”

Section: Computational Methodsmentioning

confidence: 99%

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Phase Relations in the Ni–S System at High Pressures from ab Initio Computations

Sagatov

Bazarbek

Inerbaev

et al. 2021

ACS Earth Space Chem.

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Based on the ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of compounds in the Ni−S system at pressures of 100−400 GPa were determined. As a result, a homologous series of discrete compounds (Ni and S) consisting of Ni 14 S-C2/m, Ni 13 S-R3̅ , Ni 12 S-R3̅ , Ni 5 S-C2/m, Ni 4 S-P1̅ , and Ni 3 S-Cmcm is revealed. We also confirmed the absence of the stable Febearing compounds between Fe and Fe 2 S in the studied pressure range. At the Earth's core pressures, 4 wt % of sulfur can be dissolved in solid fcc-Ni without deformation of the structure. Significant deformations in the Ni structure occur at sulfur contents from 4 to 15 wt %. In contrast, up to 0.45 wt % of sulfur could be dissolved in hcp-Fe at 350 GPa and 0 K. For Ni 3 S, two phases with space groups I4̅ and Cmcm were predicted. Ni 3 S-I4̅ is stable at least from 100 GPa, whereas above 330 GPa, it transforms into Ni 3 S-Cmcm. The pressure of phase transition is almost independent of temperature. The Ni 2 S is stable in the entire pressure range and undergoes a single-phase transition from the Pnma-to P6̅ 2m-phase at 266 GPa and 0 K with a Clapeyron slope of 5 MPa/ K. The S-rich sulfide NiS 3 is characterized by Im3̅ m symmetry and is thermodynamically stable from 100 to 318 GPa. Our new data on Ni sulfides might be important to constrain detailed thermodynamic models for Fe−Ni-bearing Earth and planetary cores.

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“…It is now possible to use ab initio quantum mechanical methods, usually based on periodic density functional theory (DFT), to study the behaviour of compounds under the high pressures and elevated temperatures of the Earth's core, allowing detailed examination of the physical, mechanical and chemical properties of these materials and complementing experimental studies (Alfe et al, 2000;Belonoshko et al, 2000;Alfè et al, 2002b;Belonoshko and Ahuja, 2003;Gavryushkin et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of structural, elastic and thermodynamic properties of Fe3S at high pressure: Implications for planetary cores

Valencia

Moya

Morard

et al. 2022

American Mineralogist

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Using density functional theory electronic structure calculations, the equation of state, thermodynamic and elastic properties and sound wave velocities of Fe3S at pressures up to 250 GPa have been determined. Fe3S is found to be ferromagnetic at ambient conditions but becomes nonmagnetic at pressures above 50 GPa. This magnetic transition changes the c/a ratio leading to a more isotropic compressibility, and discontinuities in elastic constants and isotropic sound velocities. Thermal expansion, heat capacity and Grüneisen parameters are calculated at high pressures and elevated temperatures using the quasiharmonic approximation. We estimate Fe-Fe and Fe-S force constants, which vary with Fe environment, as well as the 56 Fe/ 54 Fe equilibrium reduced partition function in Fe3S and compare these results with recently reported experimental values. Finally, our calculations under the conditions of the Earth's inner core allow us to estimate a S content of 2.7 wt%S, assuming the only components of the inner core are Fe and Fe3S, a linear variation of elastic properties between end-members Fe and Fe3S and that Fe3S is kinetically stable. Possible consequences for the core-mantle boundary of Mars are also discussed. This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Stability of B2‐type FeS at Earth's inner core pressures

Cited by 10 publications

References 37 publications

Partitioning of sulfur between solid and liquid iron under Earth’s core conditions: Constraints from atomistic simulations with machine learning potentials

Partitioning of sulfur between solid and liquid iron under Earth’s core conditions: Constraints from atomistic simulations with machine learning potentials

Phase Relations in the Ni–S System at High Pressures from ab Initio Computations

Ab initio study of structural, elastic and thermodynamic properties of Fe3S at high pressure: Implications for planetary cores

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