Ab initio structure modeling of ZrO2 nanosheets and single-wall nanotubes

We employed first-principles simulations using hybrid exchange–correlation density functional PBE0 within LCAO approximation to investigate the properties of ZrO2 nanotubes constructed from the different zirconia polymorphs, in an attempt to understand the relation between the bulk zirconia atomic structure and the stability of zirconia nanotubes. For the rolling of nanotubes we used the relaxed or reconstructed thin slabs obtained by cleaving cubic, tetragonal and monoclinic zirconia parallel to all possible low-index faces. The structure of nanotubes has been optimized with respect to unit cell constant and intracell degrees of freedom consistent with the initial rotohelical symmetry. The calculated nanotube formation and strain energies show that the most stable tubes with thin (one ZrO2 layer) walls originated from the hexagonal (1 1 1) nanosheets of the cubic fluorite phase. The tubes with walls composed of two ZrO2 layers, most likely have lepidocrocite morphology. The tubes with thicker walls can possess a different structure originating from cubic, tetragonal or orthorhombic phases. The comparison of similar zirconia and titania nanotubes provides evidence that zirconia nanotubes are more stable relative to the precursor nanosheets, while titania nanotubes are more stable relative to the parent bulk phases.