Two-dimensional thermodynamic theory of epitaxialPb(Zr,Ti)O3thin films

Effects of film stresses on the phase stability and various ferroelectric properties of the epitaxially oriented $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_3$ thin film were theoretically investigated. For this purpose, a two-dimensional thermodynamic model was developed using the Landau-Devonshire phenomenological theory. The theoretical computation predicts an increase in the para-ferroelectric transition temperature and an enhanced thermodynamic stability of the tetragonal-phase field, irrespective of the sign of stress (i.e., both tensile and compressive). In particular, it is predicted that tensile stress makes a new ferroelectric orthorhombic phase stable. We have also shown that dielectric properties usually exhibit their maximum values at a newly established Zr-rich morphotropic phase boundary, except for those parallel to the direction of the spontaneous polarization.