Atomic Resolution Analysis of the Defect Chemistry and Microdomain Structure of Brownmillerite‐Type Strontium Cobaltite

To investigate the fundamental aspects of vacancy ordering in oxygen‐transporting ceramic membranes, we have performed atomic resolution analysis of individual domains in brownmillerite‐type SrCoO 3−δ . Electron energy loss spectroscopy indicates that the Co valence state in adjacent planes can be 2+ and 4+. This charge localization is accompanied by oxygen deficiency and the formation of ordered octahedral and tetrahedral coordinated Co sites. At microdomain boundaries, Z ‐contrast images reveal a structural relaxation of the octahedral site with the reduction of the Co valence state from 4+ to 3+ and the incorporation of extra oxygen vacancies.