Mechanically induced defects and strength of BN nanotubes

We identify, by dislocation theory and molecular dynamics simulations, possible dislocation dipoles (5\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 he 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.