Microscopic structure and migration of 90 degrees ferroelectric domain wall in BaTiO3 determined via molecular dynamics simulations

BaTiO3 is a well-known piezoelectric material with commercial uses. The ferroelectric state of BaTiO3 generally comprises electrically polarized domains separated by domain walls (DWs). The DW alters local polarization vectors by an angle of 90 degrees for 90 degrees DW or 180 degrees for 180 degrees DW. The DW is crucial to piezoelectric properties such as response time and fatigue. Furthermore, the DW structure and its dynamics in BaTiO3 are not well understood. Hence, for the first time, we theoretically obtained the atomistic structure of the 90 degrees DW via molecular dynamics simulations at 300 K with the core-shell interatomic potential, using a large-scale system with a side length of 2.8 x 10(3) angstrom. The width of the 90 degrees DW thereby obtained was approximately 30 angstrom, which was 20 angstrom wider than that of the 180 degrees DW. Under the external electric field E(sic)(ext) parallel to the DW, we observed an extension of a domain having a polarization vector with a positive component along the E(sic)(ext)-direction. The migration velocity of the 90 degrees DW was approximately two times that of the 180 degrees DW at the same Eext in the range 7 - 20 MV / m. For E-->(ext) >= 15 MV/m, the migration velocity of the 90 degrees DW in the direction with a positive component along the polarization vector of the extending domain was substantially higher than that in the opposite direction. The physical causes of the difference in the migration velocities of the 90 degrees DW in the two directions were analyzed.