CeNbO_4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO₄, CeNbO_4.08, CeNbO_4.25, CeNbO_4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades. However, the oxide ionic transport mechanism has remained unclear due to the unknown atomic structures of CeNbO_4.08 and CeNbO_4.33. Here, we report the complex (3 + 1)D incommensurately modulated structure of CeNbO_4.08, and the supercell structure of CeNbO_4.33 from single nanocrystals by using a three-dimensional electron diffraction technique. Two oxide ion migration events are identified in CeNbO_4.08 and CeNbO_4.25 by molecular dynamics simulations, which was a synergic-cooperation knock-on mechanism involving continuous breaking and reformation of Nb₂O₉ units. However, the excess oxygen in CeNbO_4.33 hardly migrates because of the high concentration and the ordered distribution of the excess oxide ions. The relationship between the structure and oxide ion migration for the whole series of CeNbO_4+δ compounds elucidated here provides a direction for the performance optimization of these compounds.

CeNbO _4+δ是一类具有不同氧含量（CeNbO ₄、CeNbO _4.08、CeNbO _4.25、CeNbO _4.33）的氧超化学计量材料，显示出混合电子和氧化物离子传导，四十年来一直为人所知。然而，由于CeNbO _4.08和CeNbO _{4.33 的}原子结构未知，氧化物离子传输机制仍不清楚。在这里，我们报告了 CeNbO _4.08的复杂 (3 + 1)D 调制结构，以及 CeNbO _4.33的超胞结构使用三维电子衍射技术从单个纳米晶体中提取。通过分子动力学模拟，在 CeNbO _4.08和 CeNbO _4.25中发现了两个氧化物离子迁移事件，这是一种协同合作的连锁反应机制，涉及 Nb ₂ O ₉单元的连续断裂和重整。然而，由于过量氧化物离子的高浓度和有序分布，CeNbO _{4.33 中}的过量氧很难迁移。这里阐明的全系列CeNbO _{4+ δ}化合物的结构与氧化物离子迁移之间的关系为这些化合物的性能优化提供了方向。