LAUSR

Oxygen vacancies (Vo) play significant roles in determining the properties of transition-metal oxides. However, the concentration of Vo cannot be tuned quantitatively by optimizing the preparation conditions, and the precise control of Vo distribution at the atomic scale is even more challenging. Here, by controlling the reversible phase transitions between perovskite LaCoO3 (PV-LCO) and brownmillerite LaCoO2.5, we realize the tuning of Vo in PV-LCO, including the concentration with quantitative precision and the spatial distribution at the atomic scale. With the first principles calculations, we clarify that two thirds of Vo in PV-LCO can be eliminated after a cycle of the reversible phase transitions, and all the residual Vo are confined in specific lattice sites in PV-LCO. Such an ordered distribution of Vo can help to enhance the ferromagnetism of PV-LCO.