Abstract
Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium, Na 2 He, which has a fluorite-Type structure and is stable at pressures >113â €..GPa. We show that the presence of He atoms causes strong electron localization and makes this material insulating. This phase is an electride, with electron pairs localized in interstices, forming eight-centre two-electron bonds within empty Na 8 cubes. We also predict the existence of Na 2 HeO with a similar structure at pressures above 15â €..GPa.
Original language | English |
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Pages (from-to) | 440-445 |
Number of pages | 6 |
Journal | Nature Chemistry |
Volume | 9 |
Issue number | 5 |
DOIs | |
State | Published - 1 May 2017 |
Externally published | Yes |