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Volumes and spin states of FeHx: Implication for the density and temperature of the Earth’s core

  • Hua Yang , Joshua M.R. Muir and Feiwu Zhang ORCID logo EMAIL logo
Published/Copyright: March 30, 2023
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American Mineralogist
From the journal American Mineralogist Volume 108 Issue 4

Abstract

Hydrogen is the most abundant element in the solar system and has been considered one of the main light elements in the Earth’s core. The hydrogen content in the Earth’s core is determined normally by matching the volume expansion caused by the incorporation of hydrogen into FeHx to the Earth’s core density deficit. The magnitude of this volume expansion at the pressure (P) and temperature (T) conditions of the Earth’s core is still unknown, and the effect of spin transition in FeHx at high pressure is usually ignored. In this study, we simulate the Fe spin transition, equation of state, and hydrogen-induced volume expansion in Fe-H binaries at high P-T conditions using density functional theory (DFT) calculations. Our results indicate that hydrogen could stabilize the magnetic properties of fcc Fe from ~10 to ~40 GPa. A volume expansion induced by hydrogen is linear with pressure except at the Fe spin transition pressure, where it collapses significantly (~30%). The fcc FeH lattice is predicted to expand at an average rate of ~1.38 and 1.07 Å3 per hydrogen atom under the Earth’s outer and inner core P-T conditions, where the hydrogen content is estimated to be ~0.54–1.10 wt% and ~0.10–0.22 wt%, respectively. These results suggest that the Earth’s core may be a potentially large reservoir of water, with up to ~98 times as much as oceans of water being brought to the Earth’s interior during its formation. Based on our predicted hydrogen content in the Earth’s core, we propose that the presence of hydrogen would induce a relatively lower core temperature, ~300–500 K colder than it has been previously speculated.

Keywords: Hydrogen; iron hydride; spin transition; volume expansion; Earth’s core; Physics and Chemistry of Earth’s Deep Mantle and Core

† Special collection papers can be found online at http://www.minsocam.org/MSA/AmMin/special-collections.html.

Funding statement: This work was supported by the National Natural Science Foundation of China (41773057, 42050410319) and Science and Technology Foundation of Guizhou Province (ZK2021-205), with computational resources from Computer Simulation Labs of IGGCAS, the National Supercomputer Center in Shenzhen, the TH-2 High-Performance Computer System in Lvliang, China.

Acknowledgments

We thank two anonymous reviewers for their constructive comments and suggestions, which greatly improved the quality of the manuscript. H.Y. thanks Prof. Yunguo Li for his fruitful discussions.

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Received: 2021-07-31
Accepted: 2022-05-06
Published Online: 2023-03-30
Published in Print: 2023-04-25

© 2023 by Mineralogical Society of America

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https://doi.org/10.2138/am-2022-8237
Keywords for this article
Hydrogen; iron hydride; spin transition; volume expansion; Earth’s core; Physics and Chemistry of Earth’s Deep Mantle and Core

Articles in the same Issue

  1. Mineralogy and geochemistry of hot spring deposits at Námafjall, Iceland: Analog for sulfate soils at Gusev crater, Mars
  2. The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure
  3. Hydrogen occupation and hydrogen-induced volume expansion in Fe0.9Ni0.1Dx at high P-T conditions
  4. Volumes and spin states of FeHx: Implication for the density and temperature of the Earth’s core
  5. Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions
  6. Structural changes in shocked tektite and their implications to impact-induced glass formation
  7. Characterization of vandenbrandeite: A potential alteration product of spent nuclear fuel
  8. The NaCl-CaCO3 and NaCl-MgCO3 systems at 6 GPa: Link between saline and carbonatitic diamond forming melts
  9. Single-crystal elasticity of (Al,Fe)-bearing bridgmanite up to 82 GPa
  10. Single-crystal X-ray diffraction of fluorapatite to 61 GPa
  11. Iron and aluminum substitution mechanism in the perovskite phase in the system MgSiO3-FeAlO3-MgO
  12. Ultrasonic studies of alkali-rich hydrous silicate glasses: Elasticity, density, and implications for water dissolution mechanisms
  13. Gadolinium-dominant monazite and xenotime: Selective hydrothermal enrichment of middle REE during low-temperature alteration of uraninite, brannerite, and fluorapatite (the Zimná Voda REE-U-Au quartz vein, Western Carpathians, Slovakia)
  14. Nucleation of Th-rich cerianite on halloysite surface in a regolith-hosted rare earth elements deposit in South China
  15. Presentation of the Dana Medal of the Mineralogical Society of America for 2022 to Cin-Ty Lee
  16. Acceptance of the Dana Medal of the Mineralogical Society of America for 2022
  17. Presentation of the Mineralogical Society of America Award for 2022 to Benjamin M. Tutolo
  18. Acceptance of the Mineralogical Society of America Award for 2022
  19. Presentation of the 2022 Roebling Medal of the Mineralogical Society of America to John W. Valley
  20. Acceptance of the 2022 Roebling Medal of the Mineralogical Society of America
  21. New Mineral Names
  22. Book Review
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