Compressional wave velocity for iron hydrides to 100 gigapascals via picosecond acoustics

Wakamatsu, Tatsuya; Ohta, Kenji; Tagawa, Shoh; Yagi, Takashi; Hirose, Kei; Ohishi, Yasuo

doi:10.1007/s00269-022-01192-8

Cited by 6 publications

(9 citation statements)

References 57 publications

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“…5). There is a discontinuity in the bulk sound velocity between NM and LMD, which is consistent with recent V P measurement on fcc FeH (Wakamatsu et al 2022). Therefore, if such magnetic transitions exist in Ganymede and Mercury core, anomalies in elastic wave velocities may be expected.…”

Section: Discussionsupporting

confidence: 89%

Magnetism and equation of states of fcc FeHx at high pressure

Gomi,

Hirose

2023

American Mineralogist

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Hydrogen is a strong candidate for light alloying elements in the terrestrial cores.Previous first-principles studies on non-stoichiometric hexagonal close-packed (hcp) and double hexagonal close-packed (dhcp) FeH x predicted a discontinuous volume expansion across the magnetic phase transition from non-magnetic (NM) or antiferromagnetic (AFM) to ferromagnetic (FM) state with increasing the hydrogen content, x at 0 K. However, previous high pressure and temperature neutron diffraction experiments on face-centered cubic (fcc) FeH x did not show such nonlinearity. The discrepancy between theory and experiment may be due to differences in the crystal structure, magnetism, or temperature. In this study, we computed the equation of states for fcc FeH x by using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation (KKR-CPA). In addition to the four types of ground-state magnetism (FM, AFM-I, AFM-II, and NM), we also calculated the local magnetic disorder (LMD) state, which approximates the paramagnetic (PM) state with local spin moment above the Curie temperature. The results show that even though FM, AFM-I, AFM-II, and NM calculations predict a discontinuity in the volume at 0 K, the volume becomes continuous above the Curie temperature, consistent with the previous high-temperature experiment. From the enthalpy comparison at 0 K, FM fcc FeH (x = 1) undergoes the NM state above ~48 GPa. The magnetic transition pressure decreases with decreasing hydrogen content. Therefore, below the magnetic transition pressure, local spin moments affect the density and elastic wave velocity of fcc FeH x , which may be important for small terrestrial bodies such as Mercury and Ganymede. On the other hand, at the Earth's core pressure above 135 GPa, fcc FeH x becomes NM. Thus, we calculated the density and bulk sound velocity as a function of pressure at 0 K for NM 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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Section: Discussionsupporting

confidence: 89%

Magnetism and equation of states of fcc FeHx at high pressure

Gomi,

Hirose

2023

American Mineralogist

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“…Compared with our MD calculated results, the experimental data extrapolated from ambient temperature by Wakamatsu et al. (2022) overvalued the density and underestimated the compressional wave velocity V p of fcc FeH at inner core conditions (Figure 4). The Debye sound velocities V d of fcc FeH are always higher than those of hcp FeH even at high temperatures of 5000 K (Figure S5 and Table S7 in Supporting Information ).…”

Section: Resultscontrasting

confidence: 60%

“…Data for Figure 3 was sourced from Dziewonski and Anderson (1981) and Wang et al (2021). Data for Figure 4 was sourced from Caracas (2015b), Dziewonski and Anderson (1981), He et al (2022b), Li et al (2018), Wakamatsu et al (2022), andWang et al (2021). Note that other citation data that do not provide Datasets are taken directly from the text or the supplementary material of the references.…”

Section: Discussionmentioning

confidence: 99%

“…2021). The extrapolated experimental data for face-centered cubic (fcc) FeH are from Wakamatsu et al (2022). The data of fcc FeH under 6000 K are fitted from data at 0, 2000, 4000, and 5000 K. The red dashed line region represents the superionic state transition temperature for hcp Fe-H (∼3000 K) (He et al, 2022a) and fcc Fe-H (∼3500 K) (Yang et al, 2022a).…”

Section: Data Availability Statementmentioning

confidence: 99%

“…Thompson et al (2018) measured the seismic properties of fcc FeH x (x ∼1) in Nuclear Resonant Inelastic X-Ray Scattering experiments up to ∼82 GPa. Wakamatsu et al (2022) determined the compressional wave velocities of fcc FeH with picosecond acoustic measurements in laser-heated diamond anvil cells (LHDAC) at pressures up to 100 GPa. All of these studies, however, were conducted at ambient temperatures but the effect of temperature is likely to be critical in Fe-H systems.…”

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confidence: 99%

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The Geophysical Properties of FeH_x Phases Under Inner Core Conditions

Yang,

Dou,

Xiao

et al. 2023

Geophysical Research Letters

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Hydrogen has been proposed as an important light element in planetary iron cores, while the crystal structure and thermoelasticity of FeHx (x = 1) (FeH hereafter) under inner core conditions remain largely unknown. Recent studies report that FeH adopts an face‐centered cubic (fcc) structure up to core conditions. In this study, using ab initio molecular dynamics, we calculate the free energy and elastic properties of FeH at high P‐T conditions. Our results indicate that the hexagonal close‐packed (hcp) structure of FeHx is favored by both the low hydrogen concentration and the elevated temperature of inner‐core conditions. We also clarify that lattice hydrogen hardens the wave velocities of iron while superionic hydrogen softens it. Both fcc‐ and hcp‐FeH can match inner‐core wave velocities and Poisson's ratio, which supports the hypothesis of hydrogen as a vital light element in the Earth's core.

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Characterization of the lattice preferred orientation of hcp iron transformed from the single-crystal bcc phase in situ at high pressures up to 80 GPa

Park,

Wakamatsu,

Azuma

et al. 2024

Phys Chem Minerals

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Studying the anisotropic physical properties of hexagonal closed-packed (hcp) iron is essential for understanding the properties of the Earth’s inner core related to the preferred orientation of the inner core materials suggested by seismic observations. Investigating the anisotropic physical properties of hcp iron requires (1) the synthesis of hcp iron samples that exhibit several distinctive types of strong lattice preferred orientation (LPO) and (2) the quantitative LPO analysis of the samples. Here, we report the distinctive LPO of hcp iron produced from single-crystal body-centered cubic (bcc) iron compressed along three different crystallographic orientations ([100], [110], and [111]) in a diamond anvil cell based on synchrotron multiangle X-ray diffraction measurements up to 80 GPa and 300 K. The orientation relationships between hcp iron and bcc iron are consistent with the Burgers orientation relationship with variant selection. We show that the present method is a way to synthesize hcp iron with strong and characteristic LPO, which is beneficial for experimentally evaluating the anisotropic physical properties of hcp iron.

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Compressional wave velocity for iron hydrides to 100 gigapascals via picosecond acoustics

Cited by 6 publications

References 57 publications

Magnetism and equation of states of fcc FeHx at high pressure

Magnetism and equation of states of fcc FeHx at high pressure

The Geophysical Properties of FeH_x Phases Under Inner Core Conditions

Characterization of the lattice preferred orientation of hcp iron transformed from the single-crystal bcc phase in situ at high pressures up to 80 GPa

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Compressional wave velocity for iron hydrides to 100 gigapascals via picosecond acoustics

Cited by 6 publications

References 57 publications

Magnetism and equation of states of fcc FeHx at high pressure

Magnetism and equation of states of fcc FeHx at high pressure

The Geophysical Properties of FeHx Phases Under Inner Core Conditions

Characterization of the lattice preferred orientation of hcp iron transformed from the single-crystal bcc phase in situ at high pressures up to 80 GPa

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The Geophysical Properties of FeH_x Phases Under Inner Core Conditions