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Department of Dielectrics

Institute of Physics of the Czech Academy of Sciences


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Theory and simulations

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Spatio-temporal distribution of relative Ti-O6 displacements in cubic BaTiO3

BaTiO3 is often considered a model ferroelectric material in which the dielectric properties are defined by the displacements of Ti ions with respect to surrounding oxygen atoms. However, despite the decades of a dedicated research, certain controversies have remained as to the description of collective movements of the Ti ions. We approached this problem using nonoscale-oriented X-ray scattering methods and large-scale atomistic simulations [1]. Together these allowed us to show that the Ti dynamics can be exhaustively explained by phonons excited on a timescale of picoseconds.

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Domain wall contribution to lattice dynamics and permittivity of BiFeO3

Ferroelectric materials are known for their exceptionally high dielectric permittivity. It turns out, that important part of it originates from a material's complicated microstructure and in particular from interfaces between ferroelectric domains.

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First-principles-based Landau-Devonshire potential for BiFeO3

We describe a first-principles-based computational strategy for determination of the Landau-Devonshire potential.

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Existence conditions for ferroaxial materials

All 212 species of structural phase transitions with a macroscopic symmetry breaking were inspected with respect to the simultaneous occurrence of the ferroelastic, ferroelectric, and ferroaxial properties.

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Ising lines: Natural topological defects within ferroelectric Bloch walls

Phase-field simulations demonstrate that the polarization order-parameter field in the Ginzburg-Landau-Devonshire model of rhombohedral ferroelectric BaTiO3 allows for an interesting linear defect, stable under simple periodic boundary conditions. This linear defect, here called the Ising line, can be described as an about 2-nm-thick intrinsic paraelectric nanorod acting as a highly mobile borderline between finite portions of Bloch-like domain walls of opposite helicity.

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Phase transition in ferroelectric domain walls of BaTiO3

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 so different. We have recently realized that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO3 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) [see Figure 1] by a compressive epitaxial stress.

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Dielectric response of a phase transition in domain wall

Computer simulations based on Ginzburg-Landau-Devonshire theory was used to study details of a phase-transition between Ising and Bloch type of a domain wall.

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Piezoelectric response of nanotwinned ferroelectric perovskites

Computer simulations based on Ginzburg-Landau-Devonshire theory has benn used to investigate piezoelectric properties of tetragonal BaTiO3 crystals. We have shown that piezoelectric response of twinned BaTiO3 increases with increasing density of 90-degree domain walls.

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