Nonlinear dielectric response of epitaxial Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript> TiO<Subscript> 3</Subscript> thin films

Based on Landau-Devonshire (LD)-type phenomenological thermodynamic theory, the electric field dependence of the dielectric properties of tetragonal single-domain barium strontium titanate(Ba<Subscript>1-x</Subscript>Sr<Subscript>x</Subscript>TiO<Subscri pt>3</Subscript>) films on cubic substrates is theoretically investigated by taking into account the high order terms of the polarization. At room temperature, the nonlinear dielectric responses of epitaxial Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</S ubscript> films are provided by adjusting the film thickness and growth temperature. The strong nonlinearity of relative dielectric constant and pyroelectric coefficient are attained around critical film thickness on MgO (69 nm) and LaAlO<Subscript>3</Subscript> (132 nm) substrates or critical growth temperature on MgO (337 °C) substrate with respect to epitaxy-induced lattice misfit and thermal stresses during deposition. This can be explained that small compressive stresses are effective to support high nonlinearity of dielectric constant and pyroelectric coefficient for Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</S ubscript> films irrespective of whether they are on compressive substrate or tensile substrate. It is also predicted that a large tunability may be achieved by altering processing conditions, such as the film thickness and growth temperature for different substrates. Our theoretical results are in good agreement with the experimental data reported in literature. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005