Influence of flexoelectric effects on domain switching in ferroelectric films

Flexoelectricity has been shown to be an effective strategy to modulate the polarization configurations, domain structures, and physical properties in nanoscale ferroelectric thin films. However, the relations between the domain switching processes and flexoelectric effects remain elusive, which is essential for the design of nanoscale ferroelectric electric devices. In this work, strain-gradient and normal PbTiO₃ films are fabricated and investigated to resolve this elusive relationship. By using large-scale and local piezoelectric force microscopy characterization, the ferroelectric domain switching in strain-gradient PbTiO₃ films is found to be hard and hindered under applied electric fields compared with the normal ones. Successive atomic-scale scanning transmission electron microscopy imaging analysis manifests that the domains in the strain-gradient PbTiO₃ films are stabilized by an additional effective strain gradient-induced flexoelectric field, which was introduced by negative pressure originated from vertically distributed Pb-rich anti-phase domains. This study proposes an effective method to stabilize the ferroelectric polarization in nanoscale ferroelectric films, thus facilitate improving the reliability of ferroelectric electronic devices.