Pressure-induced structural phase transition of small-diameter carbon nanotubes

We study pressure-induced structural phase transition of carbon nanotube solids using the constant-pressure tight-binding molecular-dynamics method. We find that the bundle with armchair nanotube transforms into a new phase consisting of so-called zigzag graphene nanoribbons and sp3 carbon atoms by applying the pressure of 10 GPa. Under higher pressure of 30 GPa, anisotropic sp3 phases possessing high hardness comparable to cubic diamond are obtained from armchair nanotube solid, whereas amorphous diamond phases are obtained from the bundle with chiral nanotubes. Using the density-functional theory, we also study electronic structure of a new sp3 phase obtained in the molecular-dynamics simulation.