Route to a novel tetragonal carbon allotrope via T-carbon

Abstract

Through first-principles calculations, we employed anisotropic compression to T-carbon and identified several carbon allotropes. Among them, we predict a novel body-centered tetragonal carbon allotrope with space group I41/amd (No. 141), in which sixteen carbon atoms comprise four- and five- and eight-membered rings within a unit cell; we name it as bct-C16-II. Phonon spectrum calculations exhibit that it is dynamically stable under pressure up to at least 100 GPa. This bct-C16-II is energetically more stable than T-carbon and the previously proposed bct-C16-I, although it has higher energy than graphite or diamond. Our calculations also show that bct-C16-II may be super-hard with Vickers hardness around 55 GPa, comparable to cubic boron nitride. Its ideal tensile and shear strength is calculated to be around 75 and 43 GPa, respectively. We simulated the transformation pathway of importance from T-carbon to this novel bct-C16-II phase. The energy barrier is estimated to be around 0.187 eV/atom, which provides a possible approach to synthesize it. The achievement of other carbon allotropes indicates that the tetrahedral units in T-carbon are not very strong under anisotropic strains that T-carbon might be considered as a good precursor to synthesize other carbon materials. The discovery of this new phase may enrich our knowledge of carbon materials and their formation mechanisms.