Molecular dynamics simulation of 90° ferroelectric domains in PbTiO₃

Using molecular dynamics (MD) simulations based on first-principles effective Hamiltonian of bulk PbTiO₃, we corroborate the occurrence of 90° ferroelectric domain structures showing that they arise as metastable states only in cooling simulations (as the temperature is lowered) and establish characteristic stability of 90° domain structure in PbTiO ₃. In contrast, such domains do not manifest in similar simulations of bulk BaTiO₃. Through a detailed analysis and comparison between PbTiO₃ and BaTiO₃, we find that the 90° domain structures are energetically favorable only in the former, and the origin of their stability lies in the polarization-strain coupling. Our analysis suggests that a possible origin of observed 90° domain structure in BaTiO₃ has to be extrinsic, such as special boundary condition and/or defect-related inhomogeneities. We present transmission electron microscopy (TEM) images of 90° domain structure in PbTiO₃, and compare the observed thickness of domain wall and size of domains with predictions of our simulations.