Detection of Nanoscale Structural Defects in Degraded Fe-Doped SrTiO3 by Ultrafast Photoacoustic Waves

Strontium titanate, SrTiO3, has been intensively investigated as a model material in defect chemistry research. The underlying mechanism of the effects associated with a large variety of defects often requires microstructure imaging. In the present work, the distribution of nanoscale structural defects in electrodegraded Fe-doped SrTiO3 (Fe:STO) single crystals is directly revealed by ultrafast photoacoustic waves. We utilized time-resolved reflectance spectra to nondestructively characterize local structural distortions near the degraded anode and cathode interfaces in both the reduced and oxidized crystals along with transmission electron microscopy to image these defects. We show that an accumulation of oxygen vacancies resulted in significant structural deformations near the degraded cathode interface of the reduced crystal. The defect distribution shows a strong dependence on oxygen vacancy concentration and diffusion within the crystals.