Interstitial hydrogen atoms in face-centered cubic iron in the Earth’s core

Daijo Ikuta, Eiji Ohtani, Asami Sano-Furukawa, Yuki Shibazaki, Hidenori Terasaki, Liang Yuan, Takanori Hattori

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Hydrogen is likely one of the light elements in the Earth’s core. Despite its importance, no direct observation has been made of hydrogen in an iron lattice at high pressure. We made the first direct determination of site occupancy and volume of interstitial hydrogen in a face-centered cubic (fcc) iron lattice up to 12 GPa and 1200 K using the in situ neutron diffraction method. The transition temperatures from the body-centered cubic and the double-hexagonal close-packed phases to the fcc phase were higher than reported previously. At pressures <5 GPa, the hydrogen content in the fcc iron hydride lattice (x) was small at x < 0.3, but increased to x > 0.8 with increasing pressure. Hydrogen atoms occupy both octahedral (O) and tetrahedral (T) sites; typically 0.870(±0.047) in O-sites and 0.057(±0.035) in T-sites at 12 GPa and 1200 K. The fcc lattice expanded approximately linearly at a rate of 2.22(±0.36) Å 3 per hydrogen atom, which is higher than previously estimated (1.9 Å 3 /H). The lattice expansion by hydrogen dissolution was negligibly dependent on pressure. The large lattice expansion by interstitial hydrogen reduced the estimated hydrogen content in the Earth’s core that accounted for the density deficit of the core. The revised analyses indicate that whole core may contain hydrogen of 80(±31) times of the ocean mass with 79(±30) and 0.8(±0.3) ocean mass for the outer and inner cores, respectively.

Original languageEnglish
Article number7108
JournalScientific reports
Volume9
Issue number1
DOIs
Publication statusPublished - Dec 1 2019
Externally publishedYes

ASJC Scopus subject areas

  • General

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