For oxygen conducting materials applied in solid oxide fuel cells and chemical-looping processes, the understanding of the oxygen diffusion mechanism and the materials' crystal structure at different stages of the redox reactions is a key parameter to control their performance. In this paper we report the first ever in situ 3D electron diffraction (ED) experiment in a gas environment and with it uncover the structure evolution of SrFeO_2.5 as notably different from that reported from in situ X-ray and in situ neutron powder diffraction studies in gas environments. Using in situ 3D ED on submicron sized single crystals, we observe the transformation under O₂ flow of brownmillerite SrFeO_2.5 with an intra- and interlayer ordering of the left and right twisted (FeO₄)_∞ tetrahedral chains (space group Pcmb) into consecutively SrFeO_2.75 with space group Cmmm (at 350 °C, 33% O₂) and SrFeO_3−δ with space group Pmm (at 400 °C, 100% O₂). Upon reduction in H₂ flow, the crystals return to the brownmillerite structure with intralayer order, but without regaining the interlayer order of the pristine crystals. Therefore, redox cycling of SrFeO_2.5 crystals in O₂ and H₂ introduces stacking faults into the structure, resulting in an I2/m(0βγ)0s symmetry with variable β.

中文翻译：

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不同气体气氛中 3D 电子衍射探索 SrFeO2.5+δ 中的拓扑氧化还原循环

对于应用于固体氧化物燃料电池和化学链过程的氧传导材料，了解氧化还原反应不同阶段的氧扩散机制和材料晶体结构是控制其性能的关键参数。在本文中，我们报告了有史以来第一个在气体环境中进行的原位3D 电子衍射 (ED) 实验，并揭示了 SrFeO _2.5的结构演化与原位X 射线和原位中子粉末衍射研究报告的显着不同在气体环境中。在亚微米级单晶上使用原位3D ED，我们观察了 O _{2下的转变}棕色米勒石 SrFeO _2.5的流动，具有左右扭曲 (FeO ₄ ) _∞四面体链（空间群Pcmb ）的层内和层间顺序进入具有空间群Cmmm的连续 SrFeO _2.75（在 350 °C，33% O ₂）和SrFeO _3−δ具有空间群Pm m（在 400 °C，100% O ₂）。在 H ₂流量减少时，晶体返回到具有层内有序的褐镁铝石结构，但没有恢复原始晶体的层间有序。因此，SrFeO _2.5晶体在 O _{2中的氧化还原循环}H ₂将堆垛层错引入结构中，导致I 2 / m (0 βγ )0 s与变量β对称。