Stabilization of monoclinic distortion in [111] epitaxial PbTiO3 films

Monoclinic distortion stabilized in a compressively strained [111] PbTiO3, for which the polarization vector is confined in a symmetry plane, is investigated using a phenomenological model. Rhombohedral to monoclinic transitions can be induced by stress normal to the film surface when flattening of energy surface reaches a critical barrier level. Two types of monoclinic states close in free energy exhibit opposite direction of induced polarization rotation. The impact of compressive stress on polarization, monoclinic shear strain, and volume change of unit cell is calculated and compared with experimental reports in the literature. Dielectric and piezoelectric anomalies are predicted in the stabilized monoclinic phase. (C) 2021 Elsevier B.V. All rights reserved.