Microstructure of epitaxial Ba _0.7 Sr _0.3TiO ₃ SrRuO ₃ bilayer films on SrTiO ₃ substrates

The thickness evolution of the microstructure of epitaxial Ba0.7 Sr0.3 Ti O3 thin films grown on SrRu O3 SrTi O3 was investigated by means of transmission electron microscopy. Within the Ba0.7 Sr0.3 Ti O3 layer, a layered structure (three sublayers) is distinguished as for the configuration of lattice strain and defects. The first sublayer extends for 3 nm from the lattice-coherent Ba0.7 Sr0.3 Ti O3 SrRu O3 interface. The second 13-nm -thick sublayer forms a semicoherent interface with the first sublayer due to the creation of a misfit dislocation network. The third sublayer extends beyond the second sublayer exhibiting a structure characterized by compact columnar features. Planar defects are formed at the boundaries between such features. The formation of a layered structure within the Ba0.7 Sr0.3 Ti O3 films is discussed in the light of the growth modes of films on lattice-mismatched substrates.