Nonstoichiometry accommodation in SrTiO₃ thin films studied by positron annihilation and electron microscopy

Accommodation of nonstoichiometry in SrTiO₃ pulsed laser deposited (PLD) films was investigated using positron annihilation lifetime spectroscopy and (scanning) transmission electron microscopy. Increasing PLD laser fluence changed the stoichiometry from Ti to Sr deficient. Cation vacancy defects were detected, and the concentration ratio of Sr to Ti vacancies, [V_Sr]/[V_Ti], was observed to increase systematically in the Sr-deficient region, although no change in the electron microscopy lattice images was detected. Increasing Ti deficiency resulted in the accommodation of SrO layers in planar defects, and in the formation of vacancy cluster defects. A change from V_Ti to V_Sr defect positron trapping was also detected.