Alignment of Ba-O divacancies as a mechanism for polarization imprint in BaTiO3 as revealed by first principles and classical molecular dynamics simulations

Periodic arrays of Ba-O divacancies in BaTiO3 were studied using both first principles calculations and molecular dynamics simulations. It is found that the 2(nd)-neighbor complexes that are aligned along the direction of the spontaneous polarization have the lowest formation energies. The symmetry between the up and down polarization states is broken, which is manifested by a vertical shift in the polarization-voltage hysteresis loop. Systems containing randomly distributed Ba-O pairs were also studied and the shift in the hysteresis loop is negligible, which suggests that the alignment of polar Ba-O divacancies is responsible for the polarization imprint in ferroelectric BaTiO3.