Dielectric tunability of (110) oriented barium strontium titanate epitaxial films on (100) orthorhombic substrates

We develop a thermodynamic model to determine the polarization, dielectric permittivity, and tunability of epitaxial ferroelectric films on orthorhombic substrates. In particular, we study the film thickness dependence of the tunability in epitaxial (110) Ba0.6Sr0.4TiO3 films on (001) NdGaO3 substrates. The analysis takes into account the thickness dependence of the internal stress state due to the anisotropic relaxation of epitaxial stresses through the formation of misfit dislocations along the two in-plane directions. We predict significant improvement in the tunability along both in-plane and out-of-plane directions of Ba0.6Sr0.4TiO3 films with increasing film thickness compared to the similar films on cubic substrates. (c) 2006 American Institute of Physics.