Phase Diagrams of Iron Hydrides at Pressures of 100–400 GPa and Temperatures of 0–5000 K

Sagatova, Dinara N.; Gavryushkin, Pavel N.; Sagatov, Nursultan E.; Medrish, I. V.; Litasov, Konstantin D.

doi:10.1134/s0021364020030108

Cited by 15 publications

(7 citation statements)

References 36 publications

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“…The stable phase is located on the convex hull with regard to a formation from basic elements. Previous research by Bazhanova et al (2012) and Sagatova et al (2020) found metastable structures with compositions Fe x H y (x > y): Fe 4 H, Fe 3 H, and Fe 2 H. We confirmed that these structures were metastable at inner core pressures using the enthalpies of formation calculated here. As shown in Figure 1, for Fe x H y with x ≤ y, FeH, FeH 3 , Fe 3 H 5 , Fe 3 H 11 , and FeH 6 were found to be stable at core pressures while the structures of FeH 7 , FeH 8 , FeH 9 , and FeH 10 are metastable as they fall outside of the convex hull (Sagatova et al, 2020;Zhang et al, 2018).…”

Section: Fe-h Binary At Ultrahigh Pressuressupporting

confidence: 89%

“…The crystal structures and stabilities of Fm

\overline{3}

m‐FeH and Pm

\overline{3}

m‐FeH 3 (Bazhanova et al., 2012); the electronic properties, and superconductivity of I4/mmm‐FeH 5 and C2/c‐FeH 6 (Kvashnin et al., 2018); and the metallic nature of C2/c‐FeH 6 (Zhang et al., 2018) have all been reported. A topological analysis and phase diagrams of Pm3m‐FeH 3 , I4/mmm‐FeH 5 , and Cmmm‐FeH 6 at high P‐T conditions have also been presented (Sagatova et al., 2020). However, these previous Fe‐H binary structure prediction studies failed to fully consider the thermal stabilities of the structures at high pressures and temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Iron Hydride in the Earth's Inner Core and Its Geophysical Implications

Yang

Muir

Zhang

2022

Geochem Geophys Geosyst

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The chemical composition of the Earth's core has attracted growing attention in the last several decades. The Earth's core is mainly composed of Fe-Ni alloys, but this alone cannot explain its seismic properties. Compared with pure liquid Fe, the density of the outer core is ∼7% less dense and the seismic velocities are ∼4% faster at the relevant P-T conditions (Komabayashi, 2014;Kuwayama et al., 2020). Solid Fe is ∼3%-5% denser than the predicted density of the inner core at the corresponding conditions (Dewaele et al., 2006;Komabayashi & Fei, 2010;Stixrude et al., 1997). The solid inner core also exhibits strong seismic anisotropy: compressional waves propagating along the polar axis are a few percent (∼3%-4%) faster than those propagating along the equatorial plane (Morelli et al., 1986;Woodhouse et al., 1986). The Earth's core contains some Ni (∼5%) but previous studies have shown that Ni would not significantly change the density of Fe or its compressibility (Lin, 2003;Martorell et al., 2013). As an explanation for these seismic and density anomalies, the presence of small amounts (a few percent) of light alloying elements such as Si, O, S, C, and H in the core has been proposed. Among these light elements, hydrogen is essential and special.Hydrogen has the highest abundance in the solar system, and therefore, it is potentially one of the main light elements in the Earth's core. H solubility in Fe increases considerably with pressure (Fukai, 1984;Ohtani et al., 2005;Okuchi, 1997) and H becomes a strong siderophile element. Studies of H partitioning between Fe and silicate phases suggested that H prefers to dissolve into the metal phase at high P-T conditions (Shibazaki et al., 2009). More recently, by conducting high-temperature and high-pressure in-situ neutron diffraction experiments, Iizuka-Oku et al. ( 2017) claimed that Fe preferentially incorporates H and this may affect other light elements partitioning into the core in later processes. Since H is the lightest element, its influence on the Earth's core density can also be significant and remarkable.The effect of H on the properties of liquid Fe in the outer core has been widely studied. Umemoto and Hirose (2015) performed first-principles molecular dynamics calculations to examine the density and sound velocity of pure liquid Fe and Fe-H alloys at outer core P-T conditions (4000-7000 K, 100-350 GPa). They found that liquid Fe with ∼1 wt% H could match the seismic properties of the outer core, which is consistent with the latest experimental findings by Thompson et al. (2018), whose results revealed that about 0.8-1.3 wt% H is required to account for the density and sound velocity of the outer core. Furthermore, Tagawa et al. ( 2016) studied the compression of Fe-Si-H alloys at core conditions in diamond anvil cell (DAC) experiments. They proposed that the density of the outer core can be explained by 0.32 wt% H and 6.5 wt% Si (Fe 0.88 Si 0.12 H 0.17 ), which supports the hypothesis that H is a vital light element in the Earth's core.

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Section: Fe-h Binary At Ultrahigh Pressuressupporting

confidence: 89%

“…The crystal structures and stabilities of Fm

\overline{3}

m‐FeH and Pm

\overline{3}

Section: Introductionmentioning

confidence: 99%

Iron Hydride in the Earth's Inner Core and Its Geophysical Implications

Yang

Muir

Zhang

2022

Geochem Geophys Geosyst

View full text Add to dashboard Cite

show abstract

“…The stable phase is located on the convex hull with regard to a formation from basic elements. Previous research by Bazhanova et al 19 and Sagatova et al 22 found metastable phases with compositions Fe x H y (x>y): Fe 4 H, Fe 3 H, and Fe 2 H. We con rmed that these phases were metastable at inner core pressures using the enthalpies of formation calculated here. As shown in Figure 1, for Fe x H y with x ≤ y, FeH, FeH 3 , Fe 3 H 5 , Fe 3 H 11 , and FeH 6 were found to be stable compounds at core pressure while the phases of FeH 7 , FeH 8 , FeH 9 , and FeH 10 are metastable as they fall outside of the convex hull 21,22 .…”

Section: Resultssupporting

confidence: 73%

“…For example, the crystal structure and stability of Fm m-FeH and Pm m-FeH 3 19 ; the electronic properties, and superconductivity of I4/mmm-FeH 5 and C2/c-FeH 6 20 ; and the metallic of C2/c-FeH 6 21 have all been reported. A topological analysis and phase diagrams of Pm m-FeH 3 , I4/mmm-FeH 5 , and Cmmm-FeH 6 at high P-T conditions have also been presented 22 . However, previous Fe-H binary structure prediction studies failed to fully consider the thermal stabilities at high pressures and temperatures, and/or neglected relevant geoscience properties such as the density and sound velocities of these hydrides and how this varies with different Fe-H structures in detail.…”

Section: Introductionmentioning

confidence: 99%

Iron Hydride in the Earth's Inner Core

Yang

Muir

Zhang

2021

Preprint

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Hydrogen is potentially a key light element in the Earth’s core. Determining the stability of iron hydride is essential for Earth's core mineralogy applications. We investigated the thermal stabilities and seismic properties of a range of Fe-H binary at core P-T conditions. It is concluded that H induces a phase change in the Fe lattice, converting it from hcp to fcc. With 1 wt.% H incorporation, the density of Fe decreases by 7.6%, both the compressional and shear wave velocities increase by 2.3% and 1.5%, respectively. The maximum H concentration is estimated to be ~0.57 wt.% to explain the density deficit of the inner core, which corresponds to 3 times as much as seawater, indicating that a large amount of water has been brought to the Earth's interior during its formation and a relatively low inner core temperature thus induced. H alongside other light elements are required to account for the geophysical observations of the Earth's inner core.

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“…On the other hand, a series of polyhydrides have also been found in which H/Fe molar ratio increases with increasing pressure: FeH 2 at 67 GPa, FeH 3 at 86 GPa, and FeH 5 at ≥130 GPa (Pépin et al., 2014, 2017). However, the polyhydrides were all synthesized at temperatures much lower (500–1500 K) than those expected for planetary interiors and some theoretical studies predict the close‐packed structured Fe‐H alloys as the most stable form up to 400 GPa (Sagatova et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

Superstoichiometric Alloying of H and Close‐Packed Fe‐Ni Metal Under High Pressures: Implications for Hydrogen Storage in Planetary Core

Piet

Chizmeshya

Chen

et al. 2023

Geophysical Research Letters

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The Earth's core is primarily composed of Fe alloyed with ∼5.5 wt.% Ni (McDonough, 2003). The observed density deficit suggests a considerable amount of light elements in the core (Birch, 1964). Hydrogen has been considered as one of the light element candidates (Poirier, 1994). Despite its dominance in planetary systems, however, the effects of hydrogen are not well understood because of experimental challenges associated with its study at high pressure-temperature (P-T). Thanks to recent technical advances, such as pulsed laser heating with gated X-ray diffraction (Deemyad et al., 2005;Goncharov et al., 2010), and an evolving vision of the important role of hydrogen in the dynamics and compositions of the interiors of a wide range of planets (Seager & Deming, 2010), the last decade has seen a surge in studies of the Fe-H system under high P-T conditions (

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Phase Diagrams of Iron Hydrides at Pressures of 100–400 GPa and Temperatures of 0–5000 K

Cited by 15 publications

References 36 publications

Iron Hydride in the Earth's Inner Core and Its Geophysical Implications

Iron Hydride in the Earth's Inner Core and Its Geophysical Implications

Iron Hydride in the Earth's Inner Core

Superstoichiometric Alloying of H and Close‐Packed Fe‐Ni Metal Under High Pressures: Implications for Hydrogen Storage in Planetary Core

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