Nonlinear Dielectric Properties of (Ba0.60, Sr0.40)TiO3 Thin Films with Anisotropic Epitaxy

Nonlinear dielectric response of (Ba0.60 Sr0.40)TiO3 epitaxial films on <100> and <110>-oriented NdGaO3 substrates were investigated as a function of film thickness. The second, fourth and sixth order permittivities were determined at 10 GHz and at room temperature from which the so-called critical field for maximum tunability was computed using a thermodynamic formalism recently developed by the authors along the principal residual misfit strain directions. It is shown that the critical field is anisotropic in the plane of the film and its magnitudes are governed by the film thickness.