Effect of antisite-like defect in ferroelectricity of SrTiO$_{3}$ films*

Ferroelectricity in thin films of nominally nonferroelectric materials such as SrTiO$_{3}$ has been widely studied. It is known that some extrinsic factors such as strain [M. P. Warusawithana et al. Science 324, 367 (2009)] and defect [H. W. Jang et al., Phys. Rev. Lett. 104, 197601 (2010), M. Choi et al., Phys. Rev. Lett. 103, 185502 (2009)] can result in the ferroelectricity of SrTiO$_{3}$ thin films. The SrTiO$_{3}$ thin films with ferroelectricity were prepared on Si (001) substrates by oxide molecular beam epitaxy. The energy dispersive x-ray spectroscopy (EDX) mapping measurement results demonstrate Sr diffuses to the interface of SrTiO$_{3}$ and Si. The cross sectional high-resolution transmission electron microscopy (HRTEM) results show that there are interstitial Ti atoms in the unit cells. The off-centered Ti from the Sr site along [100] or [110] direction can be regarded as a polar defect pair composed of a Sr vacancy and an interstitial Ti. It is predicted that Ti antisitelike defects in SrTiO$_{3}$ are responsible for the ferroelectricity . Such antisitelike defects observed in SrTiO$_{3}$ films are considered as the origin of the ferroelectricity.