Atomic structure and electronic properties of planar defects in SrFeO3−δ thin films

Abstract

Extended planar defects found in epitaxially grown $\mathrm{SrFe}{\mathrm{O}}_{3\text{\ensuremath{-}}\ensuremath{\delta}}$ thin films are expected to exhibit distinct conductivity properties. Here, we use a combination of scanning transmission electron microscopy techniques and electron energy-loss spectroscopy (EELS) to uncover the peculiar structure of these planar defects and to explore their electronic properties. We find that the defects are formed by $\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{2+\ensuremath{\alpha}}$ layers consisting of $\mathrm{Fe}{\mathrm{O}}_{5}$ polyhedra alternating with SrO and $\mathrm{Fe}{\mathrm{O}}_{2}$ perovskite-type layers, analogous to the $\mathrm{S}{\mathrm{r}}_{4}\mathrm{F}{\mathrm{e}}_{6}{\mathrm{O}}_{12+\ensuremath{\delta}}$ crystal structure. Our experimental and theoretical EELS data, combined with projected density of states calculations, reveal peak width changes and energies shifts, which suggest an increased electron doping of the Fe $3d{e}_{g}$ band in the $\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{2+\ensuremath{\alpha}}$ layers as compared to the $\mathrm{SrFe}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ film. Thus we show that the presence of $\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{2+\ensuremath{\alpha}}$ planar defects indeed can effectively modify the electron-hole conductivity in $\mathrm{SrFe}{\mathrm{O}}_{3\text{\ensuremath{-}}\ensuremath{\delta}}$ films.