Structural characterization of laser ablated epitaxial (Ba_0.5Sr_0.5)TiO₃ thin films on MgO(001) by synchrotron X-ray scattering

Epitaxial (Ba_0.5Sr_0.5)TiO₃ thin films of two different thickness (approximately 25 and approximately 134 nm) on MgO(001) prepared by a pulsed laser deposition method were studied by synchrotron x-ray scattering measurements. The film grew initially with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became significantly rougher, but the interface between the film and the substrate did not. In the early stage of growth, the film was highly strained in a tetragonal structure (c/a = 1.04) with the longer axis parallel to the surface normal direction. As the growth proceeded further, it relaxed to a cubic structure with the lattice parameter near the bulk value, and the mosaic distribution improved significantly in both in- and out-of-plane directions. The thinner film (approximately 25 nm) showed only one domain limited mainly by the film thickness, but the thicker film (approximately 134 nm) exhibited three domains along the surface normal direction.