title: The unusual and the expected in the Si/C phase diagram.
abstract: In the Si/C phase diagram, the only stable phases at P = 1 atm are the numerous polytypes of the simplest 1:1 stoichiometry, SiC. However, many metastable yet likely to be kinetically persistent phases can be found for almost any composition. Given the instability of simple graphite-type structures with considerable Si content, we thought these metastables would be only of the diamondoid class. Indeed they are for Si3C, a stoichiometry we studied on the silicon-rich side of the phase diagram. Yet on the carbon-rich side, which we chose to explore computationally with SiC3, there was a surprise in store, a series of unusual metastable structures. The most striking of these had the appearance of a collapsed graphite structure, with benzenoid C6 units and SiSi bridges between layers. This SiC3 structure is related to known meta-(1,3,5)cyclophanes. Three other metastable structures featured layers with all carbon polyene and polyphenylene arrays. Some of these can be metallic, as we have found.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Guoying
authors.initials: G
authors.lastname: Gao
authors.forename: N W
authors.initials: NW
authors.lastname: Ashcroft
authors.forename: Roald
authors.initials: R
authors.lastname: Hoffmann