Fyzikální ústav Akademie věd ČR

Computer simulations based on Ginzburg-Landau-Devonshire theory have been used to investigate piezoelectric properties of tetragonal BaTiO₃ crystals. We have shown that piezoelectric response of twinned BaTiO₃ increases with increasing density of 90° domain walls. A considerable enhancement of the longitudinal piezoelectric coefficient is predicted for domain sizes below 50 nm. We have also shown that main contribution to the longitudinal piezoelectric coefficient comes from the volume of domains, rather than from the domain wall region [J. Hlinka et al., Nanotechnology 20, 105709 (2009)]. (more...)

Fig. 1: Dependence of the effective longitudinal piezoelectric coefficient on domain size calculated from the response of the ideal 2D laminar domain structure to weak uniaxial stresses applied along the [111] crystallographic direction. The inset shows the geometry of the initial 2D laminate domain structure assumed in the simulations.

Nevertheless, the experimentally reported impact of domain wall density is even stronger than in our simulations. Our most recent theoretical investigations[P. Marton et al., Phys. Rev. B 81, 144125 (2010) ] suggest that ferroelectric perovskites such as BaTiO3 most likely support also more exotic domain walls, resembling Bloch walls known from ferromagnetism. This kind of domain walls might account for additional enhancement of the electromechanical material response.

Fig. 2:Set of mechanically compatible and electrically neutral domain walls in the three ferroelectric phases of BaTiO₃. Letter denominating the phase (T, O and R stay for tetragonal, orthorhombic and rhombohedral phase, resp.) is followed by an angle between the polarization in adjacent domains and in some cases also by the domain-wall normal.