Body-Centered TetragonalC4: A Viablesp3Carbon Allotrope

Abstract

We have investigated by first principles the electronic, vibrational, and structural properties of bct ${\mathrm{C}}_4$, a new form of crystalline $s{p}^3$ carbon recently found in molecular dynamics simulations of carbon nanotubes under pressure. This phase is transparent, dynamically stable at zero pressure, and more stable than graphite beyond 18.6 GPa. Coexistence of bct ${\mathrm{C}}_4$ with $M$ carbon can explain better the x-ray diffraction pattern of a transparent and hard phase of carbon produced by the cold compression of graphite. Its structure appears to be intermediate between that of graphite and hexagonal diamond. These facts suggest that bct ${\mathrm{C}}_4$ is an accessible form of $s{p}^3$ carbon along the graphite-to-hexagonal diamond transformation path. DOI: http://dx.doi.org/10.1103/PhysRevLett.104.125504 © 2010 The American Physical Society