Hexagonal Close-packed Iron Hydride behind the Conventional Phase Diagram

Akihiko Machida, Hiroyuki Saitoh, Takanori Hattori, Asami Sano-Furukawa, Ken ichi Funakoshi, Toyoto Sato, Shin ichi Orimo, Katsutoshi Aoki

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


Hexagonal close-packed iron hydride, hcp FeHx, is absent from the conventional phase diagram of the Fe–H system, although hcp metallic Fe exists stably over extensive temperature (T) and pressure (P) conditions, including those corresponding to the Earth’s inner core. In situ X-ray and neutron diffraction measurements at temperatures ranging from 298 to 1073 K and H pressures ranging from 4 to 7 GPa revealed that the hcp hydride was formed for FeHx compositions when x < 0.6. Hydrogen atoms occupied the octahedral interstitial sites of the host metal lattice both partially and randomly. The hcp hydride exhibited a H-induced volume expansion of 2.48(5) Å3/H-atom, which was larger than that of the face-centered cubic (fcc) hydride. The hcp hydride showed an increase in x with T, whereas the fcc hydride showed a corresponding decrease. The present study provides guidance for further investigations of the Fe–H system over an extensive x–T–P region.

Original languageEnglish
Article number12290
JournalScientific Reports
Issue number1
Publication statusPublished - 2019 Dec 1


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