Abstract
The crystal structures of the recently discovered nonmolecular phases of are still the subject of intense debate. Based on density-functional theory calculations, we show that a layered structure (space group ) with carbon in tetrahedral coordination is thermodynamically stable between 200 and 900 GPa. The Raman spectrum for this phase agrees with that measured for . Contrary to , where octahedral coordination for silicon starts with stishovite at about 10 GPa, we find that structures with carbon in octahedral coordination are unlikely to be thermodynamically stable in at pressures currently reachable in the laboratory. We attribute the exceptional stability of tetrahedral structures in to the small atomic size of the carbon atom, which allows it to occupy the tetrahedral interstitial sites of the close-packed oxygen sublattices.
- Received 4 March 2009
DOI:https://doi.org/10.1103/PhysRevB.79.144102
©2009 American Physical Society