A structural model of carbon nanocoils (CNCs) on the basis of carbon nanotubes (CNTs) was proposed. The Young’s moduli and spring constants of CNCs were computed and compared with those of CNTs. Upon elongation and compression, CNCs exhibit superelastic properties that are manifested by the nearly invariant average bond lengths and the large maximum elastic strain limit. Analysis of bond angle distributions shows that the three-dimensional spiral structures of CNCs mainly account for their unique superelasticity.
Stable structures of pentagonal BxNy monolayers of different stoichiometric ratios were investigated through density functional theory calculations. Combining the energy and phonon dispersion, two stable pentagonal BxNy structures, B2N4‒I and B3N3‒I, are predicted. Under uniaxial and biaxial tensile strains, B2N4‒I and B3N3‒I show anisotropy mechanical behaviours in terms of Young’s modulus and intrinsic strength. B2N4‒I possesses larger Young’s modulus (up to 206 N/m) and intrinsic strength (up to 40 GPa) compared with those of B3N3‒I. Particularly, due to the low symmetry and prominent anisotropy, uniaxial tensile strain can uniquely tailor the band gap and trigger the transition from a direct to an indirect band gap in semiconducting B3N3‒I.
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