Impact of stress and long-range interaction on ultrathin ferroelectric films

Based on the Landau-Devonshire type theory, the polarization, critical thickness, pyroelectric coefficient and correlation length of epitaxial ultrathin ferroelectric BaTiO3 films with first-order phase transition have been investigated using the finite difference method. The theory not only allows for the influence of the stress attributed to lattice constant misfit between the ferroelectric film and the thick substrate, but also takes into account the long-range dipole-dipole interactions. It is shown that both the compressive stress and the long-range interaction increase the polarization and the Curie temperature, which can be compared with the experimental results, whereas the tensile stress reduces the polarization. In addition, both the stress and long-range interaction remarkably affect the pyroelectric coefficient and the correlation length.