Through first-principles calculations, the role of Ti antisitelike defects in the electrical and optical properties of ${\mathrm{SrTiO}}_3$ is proposed. Significant Ti off-centering from the Sr site toward the [100] or [110] direction leads to switchable polar states, and attractive interactions with the O vacancy drive them to form defect pairs. In these defect configurations, localized electronic states are introduced below the conduction band minimum. Our findings on Ti antisitelike defects suggest that they are responsible for the ferroelectricity and blue light emission in nonstoichiometric ${\mathrm{SrTiO}}_3$.

• Received 22 May 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.185502