Orientation-dependent structural phase diagrams and dielectric properties of PbZr_1-x Ti_x O₃ polydomain thin films

The orientation-dependent equilibrium ferroelectric domain structures and dielectric properties of polydomain PbZr_1-xTi_xO₃ thin films are investigated using a phenomenological Ginzburg-Landau-Devonshire thermodynamic model. We develop and describe three-dimensional polydomain models for (001)-, (101)-, and (111)-oriented films and explore the evolution of the structure and dielectric permittivity of the system as a function of epitaxial strain across the composition range 0.5 ≤ x ≤ 1.0. Our studies reveal that the film orientation, epitaxial strain, and composition can combine in unexpected ways to drive exotic phase stability and transformations which have intriguing implications for the properties. In particular, in (101)- and (111)-oriented films, the application of epitaxial strains along non-〈001〉-type crystallographic directions significantly reduces the stability range of the parent tetragonal phase [which is dominant in (001)-oriented films] and results in a variety of new symmetries. We also observe that the film orientation can be used to tune the relative fraction of intrinsic (i.e., within a domain) and extrinsic (i.e., from domain wall motion) contributions to the dielectric permittivity. Ultimately these studies reveal how composition, epitaxial strain, and film orientation provide for comprehensive control of the structure and properties of ferroelectrics.