Minimum tetragonality in PbTiO3/BaTiO3 ferroelectric superlattices

PbTiO3/BaTiO3 ferroelectric superlattices commensurately constrained by a SrTiO3 substrate are studied using both phenomenological theory and phase field simulations. It is found that the spontaneous polarization of the superlattice does not vary significantly with volume fraction until PbTiO3 becomes the majority of the superlattice. A minimum tetragonality exists at room temperature when the PbTiO3 volume fraction is around 90%, resulted from its different sensitivity to epitaxial strains and the electrostatic coupling of the two polarized layers in this PbTiO3/BaTiO3 superlattice.