In the recent work of Prof. Qingbo Yan et al., a structurally stable crystalline carbon allotrope, i.e., ‘T-carbon’, was predicted by means of the first-principle calculations. This allotrope can be derived by substituting each atom in diamond with a carbon tetrahedron, and possesses the same space group Fd3̅ m as diamond. The calculations on geometrical, vibrational, and electronic properties reveal that T-carbon, with a considerable structural stability and a much lower density 1.50 g/cm3, is a semiconductor with a direct band gap about 3.0 eV, and has a Vickers hardness 61.1 GPa lower than diamond but comparable with cubic boron nitride.
(See http://prl.aps.org/abstract/PRL/v106/i15/e155703)
