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Nat Chem. 2017 May;9(5):440-445. doi: 10.1038/nchem.2716. Epub 2017 Feb 6.

A stable compound of helium and sodium at high pressure.

Author information

1
School of Physics and MOE Key Laboratory of Weak-Light Nonlinear Photonics, Nankai University, Tianjin 300071, China.
2
Center for High Pressure Science and Technology Advanced Research, Beijing 100193, China.
3
Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, USA.
4
Skolkovo Institute of Science and Technology, 3 Nobel Street, Moscow 143026, Russia.
5
Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny city, Moscow Region 141700, Russia.
6
International Centre for Materials Discovery, Northwestern Polytechnical University, Xi'an 710072, China.
7
Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA.
8
Key Laboratory of Materials Physics and Center for Energy Matter in Extreme Environments, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.
9
Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, PO Box 808 L-350, Livermore, California 94550, USA.
10
Sobolev Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, 3 Pr. Ac. Koptyga, Novosibirsk 630090, Russia.
11
Istituto di Scienze e Tecnologie Molecolari del CNR (CNR-ISTM) e Dipartimento di Chimica, Universita' di Milano, via Golgi 19, Milan 20133, Italy.
12
Chair of Solid-State and Quantum Chemistry, RWTH Aachen University, Aachen D-52056, Germany.
13
Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA.
14
Photon Science DESY, Hamburg D-22607, Germany.
15
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
16
Chemistry Department, Faculty of Science, RUDN University, 6 Miklukho-Maklaya Street, Moscow 117198, Russia.
17
Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.

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, Na2He, which has a fluorite-type structure and is stable at pressures >113 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 Na8 cubes. We also predict the existence of Na2HeO with a similar structure at pressures above 15 GPa.

PMID:
28430195
DOI:
10.1038/nchem.2716

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