Oxygen is in many ways a unique element: It is the only known diatomic molecular magnet, and it exhibits an unusual O 8 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 H 2, N 2, F 2, Cl 2, Br 2, and I 2 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 I4 1/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-O 8 phase or the isostructural superconducting ζ-O 8phase 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 O 8 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.
CITATION STYLE
Zhu, L., Wang, Z., Wang, Y., Zou, G., Mao, H. K., & Ma, Y. (2012). Spiral chain O 4 form of dense oxygen. Proceedings of the National Academy of Sciences of the United States of America, 109(3), 751–753. https://doi.org/10.1073/pnas.1119375109
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