Atomistic study of stress-induced switching of 90° ferroelectric domain walls in PbTiO3: size, temperature and structural effect

Molecular dynamics simulations based on the shell model potential for PbTiO3 were carried out to investigate the effect of the cell dimension, temperature and kink structure on the domain switching of 90 degrees ferroelectric domain walls. It was found that the critical shear stress is linearly dependent on the inverse of the cell dimension, which is identified as a manifestation of the artificial electric field caused by the periodic boundary conditions. Ab initio density functional theory calculations were carried out to confirm this effect and a similar result was observed. Finite temperature simulations based on a molecular dynamics approach have shown a reduction in the critical shear stress and maximum shear strain due to the increase in thermal agitation. At a finite temperature, the domain wall structure is characterized by perovskite units cells with a preferential polarization along the < 0 1 1 >-direction. Simulations of kink structures revealed a long-range strain field caused by local disorder of the crystal lattice in the area surrounding the kink. As a direct consequence, careful size considerations on the separation distances between kinks have to be made prior to performing shear strain simulations. It was found that kink structures significantly facilitate the motion of 90 degrees domain walls in PbTiO3.