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Synthesis of FeH5: A layered structure with atomic hydrogen slabs

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Science  28 Jul 2017:
Vol. 357, Issue 6349, pp. 382-385
DOI: 10.1126/science.aan0961

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Atomic hydrogen with an iron assist

Metal polyhydrides can be used at lower pressures to make material that might have atomic hydrogen bonding. Pépin et al. manage to synthesize an incredibly hydrogen-rich FeH5 compound at 130 GPa pressure. The material consists of slabs of four thin planes of atomic hydrogen intercalated with layers of quasicubic FeH3 units. These metal polyhydrides were stable at far more accessible pressures than pure hydrogen. This achievement provides an opportunity to investigate special electrical properties expected from atomic hydrogen bonding, such as superconductivity.

Science, this issue p. 382

Abstract

High pressure promotes the formation of polyhydrides with unusually high hydrogen-to-metal ratios. These polyhydrides have complex hydrogenic sublattices. We synthesized iron pentahydride (FeH5) by a direct reaction between iron and H2 above 130 gigapascals in a laser-heated diamond anvil cell. FeH5 exhibits a structure built of atomic hydrogen only. It consists of intercalated layers of quasicubic FeH3 units and four-plane slabs of thin atomic hydrogen. The distribution of the valence electron density indicates a bonding between hydrogen and iron atoms but none between hydrogen atoms, presenting a two-dimensional metallic character. The discovery of FeH5 suggests a low-pressure path to make materials that approach bulk dense atomic hydrogen.

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