Structural and electronic properties of T-graphene and its derivatives

Abstract

Recent years there has been aroused a growing interest in designing two-dimensional (2D) structures of carbon allotropes, owing to the great success in graphene. The T-graphene is a newly proposed 2D carbon allotrope possessing tetragonal symmetry other than hexagonal symmetry of graphene. Also, the energetic and dynamical stabilities of T-graphene have been revealed. So motivated, we investigate the structural stabilities and electronic properties of T-graphene and especially its derivatives-n(n=1-5) by using the first-principle calculation based on the density function theory. By changing the atomic number (n) of the linear carbon chains connecting the two tetragon rings of T-graphene, a series of sp-sp2 hybrid structures can be formed, which is named T-graphene derivatives-n. The calculation results show that the structural stabilities, chemical bond types and electronic structures of these materials depend greatly on the parity of n. Owing to a strong π-bond formed by eight carbon atoms in T-graphene, it becomes the one with the lowest energy in all these materials studied in this work. An interesting phenomenon is found that the T-graphene derivatives-n with even n are dynamically stable as witnessed by the calculated phonon spectra without imaginary modes, while those with odd n are dynamically unstable. The metallic behaviors are present in the T-graphene derivatives-n with even carbon atoms in the linear carbon chains, showing an alternating single and triple C–C bonds. Besides, we observe that the metallicity of the T-graphene derivatives-n with even n becomes stronger as n increases. On the other hand, the linear carbon chains with odd carbon atoms are comprised of continuous C=C double bonds. These T-graphene derivatives-n with odd n also show metallic behaviors, but turn into magnetic materials (except for n=1), the magnetic moments are about 0.961μB (n=3) and 0.863μB (n=5) respectively, and ferromagnetic ordering is the only possibility for the magnetism, which rarely occurs in carbon material. Our first-principle studies indicate that the introducing carbon chains between the tetragonal carbon rings of T-graphene constitute an efficient method to obtain new two-dimensional carbon allotrope. With different numbers (even or odd) of carbon atoms on the chains, the constructed 2D carbon allotropes could show contrasting dynamical and magnetic properties. These findings provide a theoretical basis for designing two-dimensional carbon materials and carbon-based nanoelectronic devices.