Abstract
The crystal structures of two molecular phases (I and III) and a polymeric phase (V) of have been investigated to 60 GPa. transforms to at 12 GPa with almost no change of density. Although persists in to at least 60 GPa at ambient temperature, it transforms when heated to 1800 K above 40 GPa to tridymite with volume change. Each carbon atom of is tetrahedrally bonded to four oxygen atoms. is likely superhard with low compressibility , similar to cubic BN.
- Received 16 June 1999
DOI:https://doi.org/10.1103/PhysRevLett.83.5527
©1999 American Physical Society