Electron Microscopy Measurement of Picometer-Level Distortion Induced Local Phonons at a Defect

Defects in oxides usually exhibit exotic properties that may be associated with local lattice dynamics. Here, at atomic spatial resolution, we directly measure phonon modes of an antiphase boundary (APB) in SrTiO3 freestanding membrane and correlate them with the picometer-level structural distortion. We find that the SrTiO3 APB introduces new defect phonon modes that are absent in bulk SrTiO3. These modes are highly sensitive to the subtle structure distortion; i.e., the SrTiO3 APB generates the local electric dipoles, forming an antiferroelectric configuration, which significantly change the frequencies of transverse optical (TO) and longitudinal optical (LO) modes. When the local phonons are correlated with the subtle structural distortion, our findings provide valuable insights into understanding the defect properties in complex oxides and essential information for their applications such as thermoelectric devices.