Article

A stable compound of helium and sodium at high pressure

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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.

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Acknowledgements

This work was supported by the China Scholarship Council (grant no. 201206200030), NSAF (grant no. U1530402), National Science Foundation (grant no. EAR-1114313), DARPA (grant no. W31P4Q1210008), Russian Science Foundation (grant no. 16-13-10459), National 973 Program of China (grant no. 2012CB921900) and Foreign Talents Introduction and Academic Exchange Program (grant no. B08040). X.F.Z. acknowledges funding from the National Science Foundation of China (grant no. 11674176). Calculations were performed at the Tianhe II supercomputer in Guangzhou and the supercomputer of the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC02-98CH10086. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR-1128799) and Department of Energy – Geosciences (DE-FG02-94ER14466). Use of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. PETRA III at DESY is a member of the Helmholtz Association (HGF). The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007- 2013) under grant agreement no. 312284. The work of E.S. was performed under the auspices of the US Department of Energy by Lawrence Livermore National Security under contract no. DE-AC52-07NA27344. A.F.G. acknowledges support from the National Natural Science Foundation of China (grant no. 21473211), the Chinese Academy of Sciences (grant no. YZ201524) and the Chinese Academy of Sciences visiting professorship for senior international scientists (grant no. 2011T2J20) and Recruitment Program of Foreign Experts. S.L. was partly supported by state assignment project no. 0330-2016-0006. A.I.B. acknowledges the support of the National Science Foundation (CHE-1361413 to A.I.B.). I.A.P. acknowledges the support of the Ministry of Education and Science of the Russian Federation (agreement number 02.a03.21.0008).

Author information

Affiliations

  1. School of Physics and MOE Key Laboratory of Weak-Light Nonlinear Photonics, Nankai University, Tianjin 300071, China

    • Xiao Dong
    • , Xiang-Feng Zhou
    •  & Hui-Tian Wang
  2. Center for High Pressure Science and Technology Advanced Research, Beijing 100193, China

    • Xiao Dong
  3. Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, USA

    • Xiao Dong
    • , Artem R. Oganov
    • , Guang-Rui Qian
    • , Qiang Zhu
    •  & Xiang-Feng Zhou
  4. Skolkovo Institute of Science and Technology, 3 Nobel Street, Moscow 143026, Russia

    • Artem R. Oganov
  5. Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny city, Moscow Region 141700, Russia

    • Artem R. Oganov
    •  & Gabriele Saleh
  6. International Centre for Materials Discovery, Northwestern Polytechnical University, Xi'an 710072, China

    • Artem R. Oganov
  7. Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA

    • Alexander F. Goncharov
    • , Elissaios Stavrou
    •  & Sergey Lobanov
  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

    • Alexander F. Goncharov
  9. Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, PO Box 808 L-350, Livermore, California 94550, USA

    • Elissaios Stavrou
  10. Sobolev Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, 3 Pr. Ac. Koptyga, Novosibirsk 630090, Russia

    • Sergey Lobanov
  11. Istituto di Scienze e Tecnologie Molecolari del CNR (CNR-ISTM) e Dipartimento di Chimica, Universita’ di Milano, via Golgi 19, Milan 20133, Italy

    • Carlo Gatti
  12. Chair of Solid-State and Quantum Chemistry, RWTH Aachen University, Aachen D-52056, Germany

    • Volker L. Deringer
    •  & Richard Dronskowski
  13. Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA

    • Vitali B. Prakapenka
  14. Photon Science DESY, Hamburg D-22607, Germany

    • Zuzana Konôpková
  15. Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA

    • Ivan A. Popov
    •  & Alexander I. Boldyrev
  16. Chemistry Department, Faculty of Science, RUDN University, 6 Miklukho-Maklaya Street, Moscow 117198, Russia

    • Ivan A. Popov
  17. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

    • Hui-Tian Wang

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Contributions

X.D. and A.R.O. designed the research. X.D., G.S. and I.A.P. performed and analysed the calculations. V.L.D. and R.D. carried out COHP analyses. A.G. designed experiments. S.L. and A.G. loaded the sample. A.F.G., E.S., S.L., V.B.P. and Z.K. performed the experiment. E.S. and A.F.G. analysed the experimental data. G.-R.Q., Q.Z., X.-F.Z. and A.I.B. assisted with calculations. All authors contributed to interpretation and discussion of the data. X.D., A.R.O., A.F.G., G.S., I.A.P., A.I.B. and H.-T.W. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Artem R. Oganov or Xiang-Feng Zhou or Hui-Tian Wang.

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