Depolarization-mediated monoclinic states in ultrathin [111] PbTiO3 epitaxial films

Stress-depolarization field phase stability map is constructed for ultrathin [111]-PbTiO3 epitaxial films coherently grown on SrTiO3. Despite a large compressive strain imposed by the substrate, rhombohedral to monoclinic transition can be induced so that the polarization vector is confined in a symmetry plane. We investigate competition of phase stability and evolution of monoclinic states by inspecting the flattened energy surface, and show that in the presence of depolarization field the critical stress for inducing low-symmetry states can be remarkably lowered. The influence of vertical stress and depolarization field on polarization, monoclinic shear strain, and volume change of unit cell are calculated for the coherent [111]-PbTiO3, and boundary conditions allowing for considerable enhancement in dielectric and piezoelectric responses are revealed. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The stress-depolarization field phase stability map for ultrathin [111]-PbTiO3 epitaxial films on SrTiO3 reveals that inducing low-symmetry states can be remarkably lowered by the presence of the depolarization field, restricting the polarization vector in a symmetry plane. Investigation of the competition of phase stability and evolution of monoclinic states shows significant enhancement in dielectric and piezoelectric responses under certain boundary conditions.