Impact of stress on oxygen vacancy ordering in epitaxial (La0.5Sr0.5)CoO3−∂ thin films

We investigate oxygen vacancy ordering in epitaxial (La0.5Sr0.5)CoO3−∂ thin films grown by sputter deposition on (001) LaAlO3 and (001) SrTiO3. After annealing at 500 °C under oxygen partial pressures greater than those used during deposition, films transform to a long-range oxygen vacancy ordered structure with orthorhombic symmetry. Observed orientation variants of the oxygen vacancy ordered structures are different for the two substrates. We discuss the relationship between film stress due to lattice and thermal mismatch with the substrate, and vacancy ordering.