Defect complexes in carbon and boron nitride nanotubes.

The effect of defect complexes on the stability, structural and electronic properties of single-walled carbon nanotubes and boron nitride nanotubes is investigated using the ab initio pseudopotential density functional method implemented in the Castep code. We found more substantial atomic relaxations in the zig-zag carbon nanotube than the armchair one. We find that the B(C)B(c) defect introduced in both zig-zag and armchair carbon nanotubes results in a semimetallic system. Similarly to the carbon nanotubes, the relaxation energies in the zig-zag boron nitride nanotubes are lower than in the armchair system. We find that creating a C(B)B(N) in the boron nitride nanotube, changes the system to metallic. The zig-zag configuration is energetically more stable than the armchair one in both the boron-rich and nitrogen-rich environments. The interaction between the carbon impurity and the antisite was investigated: we find that C(B)B(N) is preferable in the B-rich environment, and C(N)N(B) is preferable in the N-rich environment. We determine that in both zig-zag and armchair systems, B(N)N(B) is stable with the heats of formation of -5.77 eV and -8.69 eV, respectively.