[Show abstract][Hide abstract] ABSTRACT: Cylindrical BaTiO3 nanorods embedded in <100>-oriented SrTiO3 epitaxial film in a brushlike configuration are investigated in the framework of the Ginzburg-Landau-Devonshire model. It is shown that strain compatibility at BaTiO3/SrTiO3 interfaces keeps BaTiO3 nanorods in the rhombohedral phase even at room temperature. Depolarization field at the BaTiO3/SrTiO3 interfaces is reduced by an emission of the 109∘ or 71∘ domain boundaries. In case of 10-80-nm diameter nanorods, the ferroelectric domains are found to form a quadruplet with a robust flux-closure arrangement of the in-plane components of the spontaneous polarization. The out-of-plane components of the polarization are either balanced or oriented up or down along the nanorod axis. Switching of the out-of-plane polarization with coercive field of about 5×106 V/m occurs as a collapse of a 71∘ cylindrical domain boundary formed at the curved circumference surface of the nanorod. The remnant domain quadruplet configuration is chiral, with the C4 macroscopic symmetry. More complex stable domain configurations with coexisting clockwise and anticlockwise quadruplets contain interesting arrangement of strongly curved 71∘ boundaries.
[Show abstract][Hide abstract] ABSTRACT: Phase-field simulations based on Ginzburg–Landau–Devonshire model were utilised to demonstrate and quantify the enhancement of the dielectric permittivity of multidomain rhombohedral BaTiO3 crystal in the vicinity of the Bloch-type to Ising-type phase transition within 180° domain boundaries with crystallographic orientation. The phase transition is driven by compressive mechanical stress applied in the plane perpendicular to the spontaneous polarisation direction. Simulations reveal a classical Curie–Weiss behaviour of the transverse component of dielectric permittivity, expected in the vicinity of a second-order phase transition.
[Show abstract][Hide abstract] ABSTRACT: Ferroelectric domain walls (FDWs) are usually considered to be of Ising type,
but there have been suggestions in recent years that Bloch-type FDWs are also
possible in some cases, e.g., in the rhombohedral phase of BaTiO3. The
mechanically compatible and electrically neutral FDWs in rhombohedral BaTiO3
are of 71-degree, 109-degree, and 180-degree type. We have investigated these
FDWs based both on first-principles calculations and on a
Ginzburg-Landau-Devonshire (GLD) model [P. Marton, I. Rychetsky, and J. Hlinka,
Phys. Rev. B 81, 144125 (2010)]. The results from both approaches confirm the
Ising nature of the 71-degree FDW and the Bloch nature of the 180-degree FDW,
and predict both Ising-type and Bloch-type FDWs are possible for the 109-degree
case. Considering the relatively small rhombohedral strain in BaTiO3, the
competition between the energies of Bloch and Ising FDWs can be discussed in
terms of a picture in which a Bloch wall is regarded as being composed of a
pair of smaller-angle Ising ones. A reduction by 40% in the parameters
describing the gradient term in the GLD model brings it into better agreement
with the first-principles results for detailed properties such as the energies
and widths of the FDWs.
[Show abstract][Hide abstract] ABSTRACT: The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175-80) explained why the structure of domain walls in ferroelectrics and ferromagnets is drastically different. Here we show that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO(3) can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones). Phase-field simulations using a Ginzburg-Landau-Devonshire model suggest that this symmetry-breaking transition can be induced by a compressive epitaxial stress. The strain-tunable chiral properties of these domain walls promise a range of novel phenomena in epitaxial ferroelectric thin films.
[Show abstract][Hide abstract] ABSTRACT: This article describes investigations of 180° walls in rhombohedral BaTiO3 in the framework of generalized Ginzburg–Landau–Devonshire model, using phase-field simulation approach. It is demonstrated that the 180° wall with the normal parallel to [1−10] direction has a Bloch-like character. Its domain profile can be understood as a pair of very close 71° and 109° walls, which can be continuously separated by a strong transverse electric field. The intermediate region can be considered as a few nanometers thick monoclinic domain.