Structure and vibrational properties of some PbTiO3-based ferroelectric superlattices

Abstract Ferroelectric PbTiO3(PTO)/BaTiO3(BTO) superlattices have been grown on SrTiO3 buffered MgO substrates by laser ablation. An extended X-ray study has shown that the orientation of individual layers is c-domain (i.e., c-axis of the tetragonal phase perpendicular to the substrate) for BTO and a-domain for PTO, contrary to what is observed for single PTO or BTO thin films, which are both c-oriented. Raman scattering reinforces this assertion, and also defines the critical modulation period A above which stress relaxation occurs via misfit dislocations. Confined modes have been also observed, in the same way as in semiconductor superlattices. The temperature variation of the soft mode frequency is shown to depend upon A.