Effects of thickness on the polarization states in epitaxial ferroelectric thin films

Abstract

The effect of thickness and depolarization field on the polarization states of epitaxial ferroelectric single-domain thin films with anisotropic in-plane misfit strains is studied by using a nonlinear thermodynamic theory with the thickness-dependent Curie temperature. The “thickness-misfit strain” phase diagrams for single-domain PbTiO3 thin films grown on tetragonal substrates are developed with and without depolarization field through minimization of the Helmholtz free energy. The results show that the depolarization field always reduces the region of the c-phase (P3 ≠ 0, P1 = P2 = 0) in the phase diagrams. The critical thickness, at which the ferroelectricity disappears, decreases when the tensile or compressive misfit strain increases.