Published November 23, 2022 | Version v1
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Topotactic redox cycling in SrFeO2.5+δ explored by 3D electron diffraction in different gas atmospheres

  • 1. University of Antwerp
  • 2. Université de Montpellier


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)N tetrahedral chains (space group Pcmb) into consecutively SrFeO2.75 with space group Cmmm (at 350 °C, 33% O2) and SrFeO3−δ with space group Pm3m (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(0 beta gamma)0s symmetry with variable beta.


Financial support is acknowledged from the FWO-Hercules fund I003218N 'Infrastructure for imaging nanoscale processes in gas/vapor or liquid environments', from the University of Antwerp through grant BOF TOP 38689. This work was supported by the European Commission Horizon 2020 NanED grant number 956099. Financial support from the French National Research Agency (ANR) through the project "Structural induced Electronic Complexity controlled by low temperature Topotactic Reaction" (SECTOR No. ANR-14-CE36-0006-01) is gratefully acknowledged.



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NanED – Electron Nanocrystallography 956099
European Commission