Abstract
Alkali metals exhibit unexpected structures and electronic behavior at high pressures. Compression of metallic sodium (Na) to 200 GPa leads to the stability of a wide-band-gap insulator with the double hexagonal structure. Post- structures remain unexplored, but they are important for addressing the question of the pressure at which Na reverts to a metal. Here, we report the reentrant metallicity of Na at the very high pressure of 15.5 terapascal (TPa), predicted using first-principles structure searching simulations. Na is therefore insulating over the large pressure range of 0.2–15.5 TPa. Unusually, Na adopts an structure at pressures of 117–125 GPa and the same structure at 1.75–15.5 TPa. The metallization of Na occurs on the formation of a stable and striking body-centered cubic electride structure consisting of icosahedra, each housing at its center about one electron that is not associated with any Na ions.
- Received 5 December 2014
DOI:https://doi.org/10.1103/PhysRevLett.114.125501
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