Ninety degree domains in RF-sputtered BaTiO3 thin films on platinum substrates

We report 90° domains in (110)-oriented polycrystalline BaTiO3 thin films. The domain and crystal structures of the thin films were investigated using transmission electron microscopy and high temperature X-ray diffraction, respectively. From X-ray diffraction, it was found that the prepared films had a (110)-preferred orientation and a tetragonal structure at room temperature. Observation in the plan-view and cross-sectional modes using transmission electron microscopy clearly indicated the presence of a 90° domain structure. In the cross-sectional mode, a 90° domain structure was observed along the film growth direction and in the plan-view mode, it was also found that a 90° domain boundary was initiated from the (111) twin boundary. The formation of a 90° domain boundary was discussed in terms of planar defects such as the (111) twin and we also proposed two kinds of stress relief mechanisms induced by 90° domain formation.