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. in particular, although the reduced low temperature phase in rare earth perovskite oxides is commonly explained in terms of ordered brownmillerite structured micro domains, its transition to the high temperature phase remains elusive. in this presentation an investigation of (La, Sr)FeO3, prepared under different reducing conditions through correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy will be shown.

We investigate the (La, Sr)FeO3 material by atomic resolution Z-contrast imaging and EELS using a 200 keV STEM/TEM JEOL2010F with a post column GIF. The combination of these techniques allows us to obtain direct images from the atomic structure of the bulk sample and to correlate this with the atomically resolved EELS information. In-situ heating of the material in a heating double tilt holder in the microscope columns allows us to simulate the highly reducing operating conditions for this oxygen conducting membrane material.