BaTiO₃‐based nanolayers and nanotubes: First‐principles calculations

Abstract

The first-principles calculations using hybrid exchange-correlation functional and localized atomic basis set are performed for BaTiO 3 (BTO) nanolayers and nanotubes (NTs) with the structure optimization. Both the cubic and the ferroelectric BTO phases are used for the nanolayers and NTs modeling. It follows from the calculations that nanolayers of the different ferroelectric BTO phases have the practically identical surface energies and are more stable than nanolayers of the cubic phase. Thin nanosheets composed of three or more dense layers of (0 1 0) and (0 1 1) faces preserve the ferroelectric displacements inherent to the initial bulk phase. The structure and stability of BTO single-wall NTs depends on the original bulk crystal phase and a wall thickness. The majority of the considered NTs with the low formation and strain energies has the mirror plane perpendicular to the tube axis and therefore cannot exhibit ferroelectricity. The NTs folded from (0 1 1) layers may show antiferroelectric arrangement of TiAO bonds. Comparison of stability of the BTO-based and SrTiO 3 -based NTs shows that the former are more stable than the latter.

Symmetry and Calculations of Nanotubes and Nanowires Based on Rutile and Perovskite Structures

“…The optimized atomic positions, square lattice constant, and energies of all considered (001) slabs generated from the cubic and tetragonal phases are the same [9]. We considered the stoichiometric slabs with the even number of atomic planes and different opposite terminations.…”

“…In our previous work [9] we have studied the BTO NTs of different thickness and chiralities obtained from (001) layers of the cubic phase and from (010) layers of the orthorhombic phase. Here we present the results for BTO NTs with the thickest walls (see Table 3), which consist of 6 densely-packed layers in the case of the cubic (tetragonal) phase and 7 densely-packed layers in the case of the orthorhombic phase.…”

“…All perovskite phases contain one formula unit in the primitive cell. Energy, structural and electronic properties of bulk perovskite phases of BTO have been calculated by us [9,17] using the same computational approach as in this study. We considered [001] NWs cut from the tetragonal and orthorhombic phases.…”

“…(2), any chirality can be achieved by rolling of the layers with the square lattice. In [9] we considered the NTs with the line group belonging to the family 11 (Ln/mmm) and to the family 13 (L(2n) n /mcm) with the chiralities (n,0) and (n,n), respectively. Unfortunately, the NTs with chiralities (n,n) rolled from the 6 densely packed layers with reliable diameters are out of scope of existing computational facilities.…”

“…All-electron basis set has been used for O atoms [5]. Small-core CRENBL pseudopotentials [6,7] have been employed for internal shells and the corresponding basis sets [6][7][8][9] have been used for the valence and virtual shells of Ti and Ba atoms. The full geometry optimization of nanosystems has been performed with preserving the main symmetry operations.…”