Size effects in epitaxial ferroelectric islands and thin films

Size effects on domain configuration and polarization switching in two-dimensional epitaxial ferroelectric islands and in thin films are investigated by using a continuum phase field model that incorporates long-range elastic and electrostatic interactions. The simulations exhibit spatial polarization distributions with different types of domain walls in the epitaxial ferroelectric islands and find two critical thicknesses, at which the simulated material changes from a multidomain state to a single-domain state and from ferroelectric phase to paraelectric phase, respectively. The two critical thicknesses and the domain wall types vary with the length-to-thickness ratio. The simulations show that macroscopic polarization switching in thin films under an external electric field is processed through the nucleation of new domains and domain wall motion. The remanent polarization and the coercive field of the simulated ferroelectric films both decrease with decreasing film thickness.