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High-Temperature Equation of State of FeH: Implications for Hydrogen in Earth’s Inner Core
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  • Shoh Tagawa,
  • Hitoshi Gomi,
  • Kei Hirose,
  • Yasuo Ohishi
Shoh Tagawa
Tokyo Institute of Technology

Corresponding Author:shoh@elsi.jp

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Hitoshi Gomi
Tokyo Institute of Technology
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Kei Hirose
The University of Tokyo
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Yasuo Ohishi
Japan Synchrotron Radiation Research Institute
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While hydrogen is one of plausible major light elements in the core, the high-temperature equation of state (EoS) of Fe-H alloy has not been experimentally examined to the core pressure range. Here we measured the volume (V) of non-magnetic (NM) fcc FeH at high pressure and temperature (P-T) to 142 GPa and 3660 K in a laser-heated diamond-anvil cell (DAC) and obtained its P-V-T EoS. An increase in the lattice volume of Fe per H atom, ΔVH, determined as functions of P and T is found to be substantially smaller than the volume of metallic H that has been used to estimate H concentration in Fe-H alloy. The ΔVH is almost identical between fcc and dhcp phases in the NM state, suggesting that it is applicable to hcp. The extrapolation of ΔVH to inner core conditions indicates its maximum H content to be 0.8–0.9 wt%.
16 Mar 2022Published in Geophysical Research Letters volume 49 issue 5. 10.1029/2021GL096260