title: High-pressure chemistry of hydrogen in metals: in situ study of iron hydride.
abstract: Optical observations and x-ray diffraction measurements of the reaction between iron and hydrogen at high pressure to form iron hydride are described. The reaction is associated with a sudden pressure-induced expansion at 3.5 gigapascals of iron samples immersed in fluid hydrogen. Synchrotron x-ray diffraction measurements carried out to 62 gigapascals demonstrate that iron hydride has a double hexagonal close-packed structure, a cell volume up to 17% larger than pure iron, and a stoichiometry close to FeH. These results greatly extend the pressure range over which the technologically important iron-hydrogen phase diagram has been characterized and have implications for problems ranging from hydrogen degradation and embrittlement of ferrous metals to the presence of hydrogen in Earth's metallic core.
authors.forename: J V
authors.initials: JV
authors.lastname: Badding
authors.forename: R J
authors.initials: RJ
authors.lastname: Hemley
authors.forename: H K
authors.initials: HK
authors.lastname: Mao