Low-symmetry monoclinic phase stabilized by oxygen octahedra rotations in thin strained EuxSr1-xTiO3 films

摘要

Using Landau-Ginzburg-Devonshire theory and phase field modeling, we explorethe complex interplay between the long-range structural order parameter (oxygenoctahedron rotations) and polarization in EuxSr1-xTiO3 thin epitaxial films. Inbiaxially tensile strained films, we discover the presence of a low symmetrymonoclinic phase with in-plane ferroelectric polarization that is stabilized byantiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable in awide temperature range, and is characterized by the large number ofenergetically equivalent polar and structural twin domains, which stimulateseasy twinning of the film and thus enhances its effective piezoelectricresponse. The flexoelectric coupling and rotostriction give rise to additionalspontaneous polarization, piezo- and pyro-electricity in the ferroelastic twinboundaries.