Phase diagram and dielectric behavior of Ba0.6Sr0.4TiO3 thin films grown on orthorhombic substrates

Using Landau–Devonshire (LD)-type phenomenological model, we investigate the phase diagrams and dielectric behaviors of single-domain single-crystal Ba0.6Sr0.4TiO3 films deposited on orthorhombic substrates. An anisotropic strain factor is introduced to quantitatively calculate the effects of anisotropic in-plane misfit strains. Investigation indicates that anisotropic strains play a crucial role on formation of stable ferroelectric phases and dielectric properties. The anisotropic strains induce tetragonal phases which only contain one in-plane spontaneous polarization component. These phases do not exist in BST films of the same composition under isotropic strains. Moreover, permittivity and tunability of films can reach to maximum when the corresponding spontaneous polarization component disappears at the boundaries of structural phase transition.