Nonorthogonal twinning in thin film oxide perovskites

We have observed nonorthogonal twinning in thin film oxide perovskites. This twinning geometry is equivalent to a 60° rotation of the twinned crystallites about the [111] direction in an [001] oriented film. This twinning is not detectable by the standard x-ray tests for film quality (a radial θ–2θ scan and a φ scan at a chi of 45°). In this study we observe this twinning in films of PbZrxTi1−xO3, BaTiO3, and SrRuO3 grown by sputtering and MOCVD on MgO and SrTiO3. These twins are observed in films deposited on a substrate with which there is a large lattice mismatch and in films that are deposited in an oxygen deficient environment. We propose that these twins result from plastic deformation associated with misfit accommodation and discuss the twin geometry and the nature of the twin interface.