Mechanically induced defects and strength of BN nanotubes

We identify, by dislocation theory and molecular dynamics simulations, possible dislocation dipoles $(5\mathrm{}|7|7|5$ and $4|8|8|4)$ as defect nuclei under tension in boron nitride nanotubes. The formation energies of the dipoles are then evaluated by ab initio gradient-corrected density functional theory. The $5|7|7|5$ dipole appears to be more favorable in spite of its homoelemental B-B and N-N bonds. Compared to carbon nanotubes, the formation energy of the primary defect is higher and remains positive at larger strain in boron nitride nanotubes, thus suggesting greater yield resistance.