A stable compound of helium and sodium at high pressure

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. © 2017 Macmillan Publisher Limited part of springer Nature. All rights reserved.

Dong X.1, 2, 3 , Oganov A.R.3, 4, 5, 6 , Goncharov A.F.7, 8 , Stavrou E.7, 9 , Lobanov S.7, 10 , Saleh G.5 , Qian G.-R.3 , Zhu Q.3 , Gatti C.11 , Deringer V.L.12 , Dronskowski R.12 , Zhou X.-F.1, 3 , Prakapenka V.B.13 , Konôpková Z.14 , Popov I.A. 15, 16 , Boldyrev A.I.15 , Wang H.-T.1, 17
Nature Publishing Group
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  • 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, NY 11794-2100, United States
  • 4 Skolkovo Institute of Science and Technology, 3 Nobel Street, Moscow, 143026, Russian Federation
  • 5 Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny city, Moscow Region, 141700, Russian Federation
  • 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, United States
  • 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 Direc., PO Box 808 L-350, Livermore, CA 94550, United States
  • 10 Sobolev Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, 3 Pr. Ac. Koptyga, Novosibirsk, 630090, Russian Federation
  • 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 Department of Solid-State and Quantum Chemistry, RWTH Aachen University, Aachen, D-52056, Germany
  • 13 Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, United States
  • 14 Photon Science DESY, Hamburg, D-22607, Germany
  • 15 Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, United States
  • 16 Chemistry Department, Faculty of Science, RUDN University, 6 Miklukho-Maklaya Street, Moscow, 117198, Russian Federation
  • 17 Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
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