Effect of anisotropic in-plane strains on phase states and dielectric properties of epitaxial ferroelectric thin films

摘要

A nonlinear thermodynamic theory is used to predict the equilibrium polarization states and dielectric properties of ferroelectric thin films grown on dissimilar substrates which induce anisotropic strains in the film plane. The "misfit strain-temperature" phase diagrams are constructed for single-domain PbTiO_3 and Pb_(0.35)Sr_(0.65)TiO_3 films on orthorhombic substrates. It is shown that the in-plane strain anisotropy may lead to the appearance of new phases which do not form in films grown on cubic substrates. The strain-induced dielectric anisotropy in the film plane is also calculated and compared with the anisotropy observed in Pb_(0.35)Sr_(0.65)TiO_3 films deposited on NdGaO_3.