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Abstract

Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium (Li; refs 1–3) and sodium (Na; refs 4, 5), leading in turn to structurally complex phases6,7,8 and superconductivity with a high critical temperature9,10,11. But the most intriguing prediction—that the seemingly simple metals Li (ref. 1) and Na (ref. 4) will transform under pressure into insulating states, owing to pairing of alkali atoms—has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at 200 GPa (corresponding to 5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to pd hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.

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References

  1. 1.

    & Pairing in dense lithium. Nature 400, 141–144 (1999)

  2. 2.

    , & Tetrahedral clustering in molten lithium under pressure. Phys. Rev. Lett. 101, 075703 (2008)

  3. 3.

    , & High pressure structures of lithium, potassium, rubidium predicted by ab initio evolutionary algorithm. Phys. Rev. B 78, 014102 (2008)

  4. 4.

    & On the constitution of sodium at higher densities. Phys. Rev. Lett. 86, 2830–2833 (2001)

  5. 5.

    , & Electronic and structural transitions in dense liquid sodium. Nature 449, 448–451 (2007)

  6. 6.

    , , & New high-pressure phases of lithium. Nature 408, 174–178 (2000)

  7. 7.

    , , , & Na at megabar pressures. Poster at 2002 High Pressure Gordon Conference (2002)

  8. 8.

    et al. Structural diversity of sodium. Science 320, 1054–1057 (2008)

  9. 9.

    , , , & Superconductivity in compressed lithium at 20 K. Nature 419, 597–599 (2002)

  10. 10.

    , , , & Superconductivity in dense lithium. Science 298, 1213–1215 (2002)

  11. 11.

    & Superconducting phase diagram of Li metal in nearly hydrostatic pressures up to 67 GPa. Phys. Rev. Lett. 91, 167001 (2003)

  12. 12.

    , & Sodium under pressure: bcc to fcc structural transition and pressure-volume relation to 100 GPa. Phys. Rev. B 65, 184109 (2002)

  13. 13.

    , , , & Melting of dense sodium. Phys. Rev. Lett. 94, 185502 (2005)

  14. 14.

    & High-pressure phases of the light alkali metals. Solid State Commun. 119, 477–490 (2001)

  15. 15.

    et al. Structure of sodium above 100 GPa by single-crystal x-ray diffraction. Proc. Natl Acad. Sci. USA 104, 17297–17299 (2007)

  16. 16.

    , & USPEX—Evolutionary crystal structure prediction. Comput. Phys. Commun. 175, 713–720 (2006)

  17. 17.

    & Crystal structure prediction using ab initio evolutionary techniques: Principles and applications. J. Chem. Phys. 124, 244704 (2006)

  18. 18.

    , & High-pressure phases of CaCO3: Crystal structure prediction and experiment. Earth Planet. Sci. Lett. 241, 95–103 (2006)

  19. 19.

    , & Structure of the metallic ζ-phase of oxygen and isosymmetric nature of the ε-ζ phase transition: Ab initio simulations. Phys. Rev. B 76, 064101 (2007)

  20. 20.

    & Self-consistent GW calculations for semiconductors and insulators. Phys. Rev. B 75, 235102 (2007)

  21. 21.

    & Crystal chemistry of the AX2 compounds under pressure. Eur. J. Solid State Inorg. Chem. 34, 785–796 (1997)

  22. 22.

    Electrides: From 1D Heisenberg chains to 2D pseudo-metals. Inorg. Chem. 36, 3816–3826 (1997)

  23. 23.

    Megabar high-pressure cells for Raman measurements. J. Raman Spectrosc. 34, 515–518 (2003)

  24. 24.

    , & Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996)

  25. 25.

    Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994)

  26. 26.

    & From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999)

  27. 27.

    & Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996)

  28. 28.

    et al. First-principles computation of material properties: The ABINIT software project. Comput. Mater. Sci. 25, 478–492 (2002); 〈

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Acknowledgements

We thank the Swiss National Science Foundation (grants 200021-111847/1 and 200021-116219), CSCS and ETH Zurich for the use of supercomputers. Parts of the calculations were performed on the Skif supercomputer (Moscow State University, Russia) and at the Joint Supercomputer Centre of the Russian Academy of Sciences (Moscow). We acknowledge partial support from DFG (grants Er 539/1/2-1) and the China 973 Program (no. 2005CB724400). Part of the experimental work was performed at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory.

Author Contributions Y.M. proposed the research and predicted the new structures. Y.M., Y.X. and A.R.O. did the calculations. M.E., I.T., S.M. and V.P. performed the experiments. Y.M., A.R.O. and M.E. contributed substantially to data interpretation and wrote the paper. A.L. wrote the latest version of the structure prediction code, and M.V. helped in data analysis. Y.M, M.E. and A.R.O contributed equally to this paper.

Author information

Author notes

    • Artem R. Oganov
    •  & Andriy O. Lyakhov

    Present address: Department of Geosciences and New York Center for Computational Science, Stony Brook University, Stony Brook, New York 11794-2100, USA.

Affiliations

  1. National Laboratory of Superhard Materials, Jilin University, Changchun 130012, China

    • Yanming Ma
    •  & Yu Xie
  2. Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Str. 10, CH-8093 Zurich, Switzerland

    • Yanming Ma
    • , Artem R. Oganov
    •  & Andriy O. Lyakhov
  3. Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany

    • Mikhail Eremets
    • , Ivan Trojan
    •  & Sergey Medvedev
  4. Geology Department, Moscow State University, 119992 Moscow, Russia

    • Artem R. Oganov
  5. Data Analysis and Visualization Services, Swiss National Supercomputing Centre (CSCS), Cantonale Galleria 2, 6928 Manno, Switzerland

    • Mario Valle
  6. Consortium for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA

    • Vitali Prakapenka

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Correspondence to Yanming Ma.

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https://doi.org/10.1038/nature07786

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