Unique temperature-dependence of polarization switching paths in ferroelectric BaTiO3: A molecular dynamics simulation study

Abstract

Polarization switching in ferroelectrics under an external electric field is crucial for their application in memory devices and actuators. Experimental research has identified two distinct polarization switching processes in tetragonal BaTiO₃ (BT) when applying an external electric field in the direction opposite to the polarization: (i) direct inversion of polarization and (ii) two-step inversion composed of two-times 90° rotation of polarization. In this study, we performed molecular dynamics simulations using accurate shell-model interatomic potential to unravel the mechanisms distinguishing these two processes. We established updated shell-model parameters by fitting them to various physical properties, including phonon dispersions obtained from density-functional theory utilizing an appropriate combination of meta-generalized gradient approximation exchange-correlation functional and dispersion force correction. When applying an external electric field in the $-c$-direction to a tetragonal BT crystal polarized along $c$-direction, the polarization switches through two-times 90° rotation at low temperatures and through formation of a polarization-inverted nucleus at high temperatures. The coercive field $E_c^{\parallel }$ along $-c$-direction increases with temperature at low temperatures, while decreases at high temperatures. In contrast, when the external electric field is applied along $b$-direction, the coercive field $E_c^{\perp }$ is smaller than $E_c^{\parallel }$ and increases monotonically with temperature. The polarization rotated in $b$-direction without nucleation along with deformation through orthorhombic structure. Unique temperature dependencies of $E_c^{\parallel }$ and $E_c^{\perp }$ are attributed to the pronounced fluctuations in local polarizations perpendicular to the system polarization and the proximity of temperature to the orthorhombic-tetragonal transition point. Present findings offer essential information in designing BT-based ferroelectrics with doping.