Topotactic redox cycling in SrFeO2.5+d explored by 3D electron diffraction in different gas atmospheres

Data, paper and SI for the publication "Topotactic redox cycling in SrFeO2.5+d explored by 3D electron diffraction in different gas atmospheres"Abstract: 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 SrFeO2.5 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 SrFeO2.5 with an intra- and interlayer ordering of the left and right twisted (FeO4)∞ tetrahedral chains (space group Pcmb) into consecutively SrFeO2.75 with space group Cmmm (at 350 °C, 33% O2) and SrFeO3−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 SrFeO2.5 crystals in O2 and H2 introduces stacking faults into the structure, resulting in an I2/m(0βγ)0s symmetry with variable β.本数据集包含发表论文《不同气体氛围下利用三维电子衍射（3D electron diffraction, ED）探究SrFeO2.5+d中的拓扑氧化还原循环》的相关数据、论文文本及补充材料（Supplementary Information, SI）。摘要：对于应用于固体氧化物燃料电池（solid oxide fuel cell）与化学链过程的氧传导材料而言，明晰其氧扩散机制以及氧化还原反应不同阶段的晶体结构，是调控其性能的核心参数。本文首次报道了气体氛围下的原位（in situ）三维电子衍射实验，并借此揭示了SrFeO2.5的结构演化过程——该过程与此前基于气体氛围下原位X射线衍射与原位中子粉末衍射（neutron powder diffraction）研究所得结果存在显著差异。通过对亚微米级单晶开展原位三维电子衍射实验，我们观察到：在氧气气流作用下，具备左、右旋(FeO4)∞四面体链层内与层间有序结构（空间群（space group）Pcmb）的钙铁石（brownmillerite）相SrFeO2.5，依次转变为空间群为Cmmm的SrFeO2.75（350 ℃、33% O2氛围）与空间群为Pmm的SrFeO3−δ（400 ℃、100% O2氛围）。在氢气气流还原过程中，该单晶会恢复为具备层内有序结构的钙铁石相，但无法复原原始单晶的层间有序结构。因此，在氧气与氢气氛围下对SrFeO2.5单晶进行氧化还原循环，会在其结构中引入层错（stacking fault），最终形成具有可变β参数的I2/m(0βγ)0s对称性结构。