Characterization of oxygen ordering in (La, Sr)FeO3-δ by atomic resolution Z-contrast imaging and electron energy-loss spectroscopy

Mixed conductors have been the focus of many studies in the last decade, leading to a detailed understanding of many of the macroscopic bulk properties of these materials. Such understanding has led to perovskite oxides being developed for several key high temperature applications. However, there are still many issues that need to be addressed on the fundamental atomic scale. in particular, although the reduced low temperature phase in rare earth perovskite oxides is commonly explained in terms of ordered Brownmillerite structured microdomains, its transition to the high temperature phase remains elusive. This paper presents a comprehensive investigation of (La, Sr)FeO3, prepared under different reducing conditions, through correlated atomic-resolution annular dark-field imaging and electron energy-loss spectroscopy. Here, the practical aspects of these combined techniques as well as their ability to characterize point defect formation and phase transitions under reducing conditions in situ in the scanning transmission electron microscope will be discussed.