Crystal structure of La0.4Sr0.6CoO2.71 investigated by TEM and XRD

The structure of the oxygen-deficient perovskite La0.4Sr0.6CoO3−δ (δ=0.29) was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Domains between 50 and 250 nm in size were observed in the electron microscope. Weak superstructure reflections were found with both X-ray and electron diffraction. Investigations of these superstructure reflections by selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED) showed that the domains in a crystal are orientated in a 90° relationship. High-resolution transmission electron microscopy (HRTEM) images from the domain boundary also revealed a 90° orientation dependency. Using the symmetry of CBED patterns, the point group 4/mmm was determined. By comparing reflections from the SAED pattern with possible reflections, the space group I4/mmm (No. 139) could be isolated and finally the crystal structure was refined by Rietveld refinement.