Atomic-scale quantification of individual oxygen vacancies and structural evolution in valence change memristors.

Elucidating the valence change mechanism in oxides memristors remains challenging due to subtle oxygen vacancy migration. Here, we quantify individual oxygen vacancies and observe their dynamic evolution during resistive switching using in-situ transmission electron microscopy. In SrNbO3.4, when fewer than 3 oxygen vacancies per unit formula form, they distribute uniformly. This solid-solution structure ensures reversible oxygen vacancy creation and annihilation. Conversely, excessive vacancies ( ≥ 3) trigger a defective structure that degrades cycling stability, while further oxygen loss induces an orthorhombic-to-cubic phase transition. If this conductive cubic phase forms a filament, the device fails permanently. By adding a thin amorphous SrNbO3 layer, we suppress interfacial oxygen loss and significantly enhance switching reversibility. This atomic-scale visualization provides direct insight into valence-change electroresistance mechanisms that are distinct from conventional filament formation models.