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Spiral chain O4 form of dense oxygen

  1. Yanming Maa,c,2
  1. aState Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China;
  2. bGeophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015; and
  3. cBeijing Computational Science Research Center, Beijing 100084, China

  1. Contributed by Ho-Kwang Mao, November 29, 2011 (sent for review November 1, 2011)

Abstract

Oxygen is in many ways a unique element: It is the only known diatomic molecular magnet, and it exhibits an unusual O8 cluster in its high-pressure solid phase. Pressure-induced molecular dissociation as one of the fundamental problems in physical sciences has been reported from theoretical or experimental studies of diatomic solids H2, N2, F2, Cl2, Br2, and I2 but remains elusive for molecular oxygen. We report here the prediction of the dissociation of molecular oxygen into a polymeric spiral chain O4 structure (space group I41/acd, θ-O4) above 1.92-TPa pressure using the particle-swarm search method. The θ-O4 phase has a similar structure as the high-pressure phase III of sulfur. The molecular bonding in the insulating ε-O8 phase or the isostructural superconducting ζ-O8 phase remains remarkably stable over a large pressure range of 0.008–1.92 TPa. The pressure-induced softening of a transverse acoustic phonon mode at the zone boundary V point of O8 phase might be the ultimate driving force for the formation of θ-O4. Stabilization of θ-O4 turns oxygen from a superconductor into an insulator by opening a wide band gap (approximately 5.9 eV) that originates from the sp3-like hybridized orbitals of oxygen and the localization of valence electrons.

Footnotes

  • ↵1L.Z. and Z.W. contributed equally to this work.

  • ↵2To whom correspondence may be addressed. E-mail: mym{at}jlu.edu.cn or h.mao{at}gl.ciw.edu.

  • Author contributions: Y.M. designed research; L.Z., Z.W., Y.W., and Y.M. performed research; L.Z., Z.W., Y.W., G.Z., H.-K.M., and Y.M. analyzed data; and L.Z., Z.W., G.Z., H.-K.M., and Y.M. wrote the paper.

  • The authors declare no conflict of interest.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1119375109/-/DCSupplemental.

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