Abstract Oxygen vacancy formation and migration in ceria is critical to its electrochemical and catalytic properties in systems for chemical and energy transformation, but its quantification is rather challenging especially at atomic-scale because of disordered distribution. Here we report a rational approach to track oxygen vacancy diffusion in single grains of pure and Sm-doped ceria at −20 °C to 160 °C using in situ (scanning) transmission electron microscopy ((S)TEM). To create a gradient in oxygen vacancy concentration, a small region (∼30 nm in diameter) inside a ceria grain is reduced to the C-type CeO1.68 phase by the ionization or radiolysis effect of a high-energy electron beam. The evolution in oxygen vacancy concentration is then mapped through lattice expansion measurement using scanning nano-beam diffraction or 4D STEM at a spatial resolution better than 2 nm; this allows direct determination of local oxygen vacancy diffusion coefficients in a very small domain inside pure and Sm-doped ceria at different temperatures. Further, the activation energies for oxygen transport are determined to be 0.59, 0.66, 1.12, and 1.27 eV for pure CeO2, Ce0.94Sm0.06O1.97, Ce0.89Sm0.11O1.945, and Ce0.8Sm0.2O1.9, respectively, implying that activation energy increases due to impurity scattering. The results are qualitatively supported by density functional theory (DFT) calculations. In addition, our in situ TEM investigation reveals that dislocations impede oxygen vacancy diffusion by absorbing oxygen vacancies from the surrounding areas and pinning them locally. With more oxygen vacancies absorbed, dislocations show extended strain fields with local tensile zone sandwiched between the compressed ones. Therefore, dislocation density should be reduced in order to minimize the resistance to oxygen vacancy diffusion at low temperatures.

中文翻译：

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通过原位透射电子显微镜定量纳米尺度跟踪单个氧化铈晶粒内的氧空位扩散

摘要氧化铈中氧空位的形成和迁移对其化学和能量转换系统中的电化学和催化性能至关重要，但由于分布无序，其量化具有挑战性，尤其是在原子尺度上。在这里，我们报告了一种使用原位（扫描）透射电子显微镜 ((S)TEM) 在 -20°C 至 160°C 下跟踪纯和 Sm 掺杂的氧化铈单晶粒中氧空位扩散的合理方法。为了产生氧空位浓度梯度，通过高能电子束的电离或辐射分解作用，氧化铈颗粒内部的一个小区域（直径约 30 nm）被还原为 C 型 CeO1.68 相。然后使用扫描纳米光束衍射或 4D STEM 以优于 2 nm 的空间分辨率通过晶格膨胀测量绘制氧空位浓度的演变图；这允许在不同温度下，在纯二氧化铈和掺钐二氧化铈内的一个非常小的域中直接确定局部氧空位扩散系数。此外，对于纯 CeO2、Ce0.94Sm0.06O1.97、Ce0.89Sm0.11O1.945 和 Ce0.8Sm0.2O1.9，氧传输的活化能确定为 0.59、0.66、1.12 和 1.27 eV。分别表示活化能因杂质散射而增加。结果得到密度泛函理论 (DFT) 计算的定性支持。此外，我们的原位 TEM 研究表明，位错通过从周围区域吸收氧空位并将它们固定在局部来阻碍氧空位扩散。随着更多的氧空位被吸收，位错显示出扩展的应变场，局部拉伸区夹在压缩区之间。因此，应降低位错密度以最小化低温下对氧空位扩散的阻力。