In situ study of the evolution of domain structure in free-standing poly-crystalline PbTiO3 thin films under external stress

The ferroelectric domain structure and its evolution with external stress in free-standing polycrystalline PbTiO3 very thin films (VTF's) (thickness t<200 nm) and thicker films (t>200 nm), have been studied by in sirtl transmission electron microscopy. It is found that the domain structure of a VTF and its dynamic response to strain are remarkably different from those of a thicker film. The VTF is composed of nanosized grains, mostly single domained. These single-domained grains manifested a strong resistance against domain formation even under high stress. On the contrary, the thicker film is composed of larger grains, mostly multidomained. The domain structure in the thicker film changes significantly with external stress. The high stability of single domains in VTF's gives a satisfactory explanation to the abnormal electrical properties of VTF's compared with those of thicker films.