in situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation.

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies ( V O ⋅ ⋅ ). Notwithstanding its significance, behaviors of the defective structure and V O ⋅ ⋅ in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce 0.88 Gd 0.12 O 2-δ ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive V O ⋅ ⋅ rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both the V O ⋅ ⋅ concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.