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

The crystal structure of SrCo0.7Fe0.2Nb0.1O2.72 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 (STEMEELS). The structure has a tetragonal P4/mmm symmetry with cell parameters a 1⁄4 b 1⁄4 ap, c 1⁄4 2ap (ap being the cell parameter of the perovskite parent structure). Octahedral BO2 layers alternate with the anion-deficient BO1.4 layers, the different B cations are randomly distributed over both layers. The specific feature of the SrCo0.7Fe0.2Nb0.1O2.72 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.