Molecular dynamics simulations of void-mediated polarization vortex domain switching in compressed BaTiO3 nanofilm

Abstract

Molecular dynamics simulations based on the anisotropic shell model with the first-principles parameters are performed to investigate the void-mediated polarization vortex domain switching in compressed BaTiO3 nanofilms. When a unit-cell-size void is located at the nanofilm center, the polarization configuration is in a single-vortex state instead of a multi-vortex state. For different void length fractions along the [100] lattice orientation, a cylindrical vortex is formed around the void while a few small vortexes nucleate closely above and/or below the void. With increasing void area fraction in the [100] plane, the vortex around the void gradually switches from clockwise to counterclockwise. Both the void shape and orientation have important effects on the vortex domain switching. A void near the model center tends to induce a clockwise vortex around it, a void in the lower left region of model to motivate a counterclockwise vortex, but a void in other locations to induce a closure domain with different switching degrees. In addition, it is found that the degree of closure domain switching could be kept if a void changes its location only in a small area. These observations should be instructive for the design and application of ferroelectric devices.