Clean and metal-doped bundles of boron-carbide nanotubes: a density functional study

Carbon nanotubes and many types of inorganic nanotubes can be produced in the form of hexagonal arrays or bundles. In this paper, we discuss results of ab initio density functional theory calculations on the stability, and atomic and electronic structure, of bundles of narrow, clean, and Li- and Cu-doped, boron-carbide nanotubes related to LiBC and CuBC layered compounds. We find that covalent bonding arises between neighboring tubes in the bundles which results in the formation of complex structures. We show that a high concentration of dopant Li atoms in the bundles can be achieved by a combination of in-tube and interstitial doping. A high concentration of Li atoms involving only in-tube doping is energetically unfavorable due to repulsive interaction between the Li atoms. By contrast, increased doping with Cu atoms can produce a metallic wirelike structure along the longitudinal axis of each tube within the bundle.