Uniaxially deformed (5,5) carbon nanotube: Structural transitions

Abstract

The Kekule structure of the ground state of (5,5) armchair carbon nanotube is revealed by semiempirical molecular orbital calculations. This structure has bonds with two different bond lengths, differing by 0.003 nm. The ground state has tripled (compared to undistorted case) translational period due to Peierls distortions. Two first order structural phase transitions controlled by the tension are predicted at zero temperature. These transitions correspond to 5% and 13% elongations of a uniaxially deformed (5,5) nanotube. The narrow gap semiconductor to metal transition is predicted at 5% elongation of the nanotube.Comment: 6 pages, 5 figure

Structural phase transition and band gap of uniaxially deformed (6,0) carbon nanotube

“…Ground state structure of (6, 0) nanotube Contrary to the armchair CNTs [6,13], the multiplication of the translational period along the nanotube axis is not necessary for zigzag CNTs with the Kekule structure. In the work [33] a possibility of Peierls gap opening was considered in the electron energy spectrum of the (3n, 0) CNTs in the dynamic regime (due to the interaction of electrons with longitudinal optical phonons at the boundary of the Brillouin zone).…”

“…We believe that the phase transition from a narrow gap to a moderate gap semiconductor is possible also at elongation of other (3n, 0) CNTs. Thus, the proposed strain sensor can be based also on (3n, 0) CNTs as well as on (n, n) armchair CNTs, where a narrow gap semiconductor to metal transition is predicted at elongation [13]. A set of (3n, 0) or Object to be controlled (insulator) (6,0) CNT Electrode = ini + obj Figure 6: The nanometer-scale strain sensor based on the stretched (6, 0) CNT.…”

“…3). At nonzero temperature, phase transitions in one-dimensional systems have a crossover char- acter (see discussion for structural phase transitions in armchair CNTs in [13] and references therein). The elastic constants (coefficient of elasticity, Poisson ratio, torsion modulus) and specific heat of the CNT also abruptly change at the phase transition.…”

“…The density functional theory calculations performed for short zigzag CNTs show that pattern of short and long bonds arise [18,19], however this pattern cannot be assigned to the Kekule structure (as it is defined in [6,20]). Previously [13] we have revealed the Kekule structure of the ground state of (5,5) armchair CNT by semiempirical molecular orbital calculations and found two deformational structural phase transitions connected with spontaneous symmetry breaking and controlled by uniaxial deformation of the CNT.…”

“…The Kekule structure can arise in a (m, n) CNT in the case that m − n is multiples of 3 [6]. The Peierls gap [6][7][8], Peierls transition temperature [5,6,[8][9][10][11][12] and bond lengths changes [6,7,13] due to Peierls distortions were estimated for (n, n) armchair CNTs. Static twist deformation of the (5,5) armchair nanotube lattice at the Peierls transition was also predicted [11,12].…”