Atomic-Scale Study of Oxygen Vacancies in Transition Metal Perovskite Oxides

Oxygen vacancies in transition metal perovskite oxides (ABO3) play the key role in controlling the functional properties of materials, such as conductivity, ferromagnetic/antiferromagnetic and electrocatalytic performance. In particular, the presence of ordered oxygen vacancies, oxygen tetrahedral/square-planer (BO4) layers, are capable of introducing crystal-chemical factors to break the initial equilibrium in the structure and highly influence those remarkable properties. During my PhD research, utilizing aberration-corrected scanning transmission electron microscopy accompanied with in-situ cooling/heating as well as ex-situ electrochemical cycling technique, I investigate the effects of ordered oxygen vacancies at the atomic scale in perovskite oxide. The crystal/electronic structure of ordered oxygen vacancies in oxygen deficient La0.5Sr0.5CoO3-ẟ thin film is demonstrated to couple with substrate SrTiO3 low temperature phase transition. The atomic arrangement of ordered oxygen vacancy domains in LaNiO3-ẟ is shown to determine the ferromagnetic/antiferromagnetic property. The formation of oxygen vacancy orderings in La1-xSrxCoO3 oxygen evolution reaction catalysts is found to facilitate the surface decomposition/corrosion, creating highly active surfaces with increase interactions with Fe impurities. The dynamics of oxygen vacancy ordering in La1-xSrxCoO3 are studied during in-situ heating in the electron microscope column to simulate the oxygen reduction evolution, serving as important reference for analyzing surface decomposition in electrochemical cycling process. Based on all the in-situ/ex-situ observation, my research advances the understanding of structure-property relationship in oxygen deficient transition metal perovskite oxides, opening up pathways for controlling the functional properties of metal oxide device and catalyst via tuning oxygen vacancies.