Layered oxygen vacancy ordering in Nb-doped SrCo1-xFexO3-δ perovskite

The crystal structure of SrCo 0.7 Fe 0.2 Nb 0.1 O 2.72 was determined using a combination of precession electron diffraction (PED), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and spatially resolved electron energy loss spectroscopy (STEM-EELS). The structure has a tetragonal P4/mmm symmetry with cell parameters a = b = a p , c = 2a p (a p being the cell parameter of the perovskite parent structure). Octahedral BO 2 layers alternate with the anion-deficient BO 1.4 layers, the different B cations are randomly distributed over both layers. The specific feature of the SrCo 0.7 Fe 0.2 Nb 0.1 O 2.72 microstructure is a presence of extensive nanoscale twinning resulting in domains with alignment of the tetragonal c-axis along all three cubic direction of the perovskite subcell.