Phononic thermal transport properties of CN nanotubes.

Reverse nonequilibrium molecular dynamics (RNEMD) is employed to study the phononic thermal transport properties of CN nanotubes. We study the effect of nanotube length and diameter on the thermal conductivity and investigate the phonon transport transition from ballistic to diffusive regime in CN nanotubes. It is found that the thermal conductivity of CN nanotubes is significantly lower than those of carbon nanotubes across the entire ballistic-diffusive range. In addition, significantly lower ballistic to diffusive transition length (72-80 nm) is observed in CN nanotubes compared to carbon nanotubes. The inspection of phonon dispersion curves shows that carbon nanotubes have stiffer acoustic modes than CN nanotubes which results in lower group velocities for CN nanotubes. Due to the presence of nitrogen atoms, the phonon mean free paths and relaxation times of CN nanotubes are shorter than those of the carbon nanotubes. The combined effect of lower group velocities and relaxation times leads to the lower thermal conductivity of CN nanotubes.