Thin film structures based on SrTiO3 and/or (Ba,Sr)TiO3 perovskite ferroelectrics exhibit a big potential for applications in tunable devices in the GHz and THz spectral range.
It has been shown recently that the strain is one of the important factors affecting the properties of ferroelectric materials. For example, it is possible to prepare epitaxial thin SrTiO3 films on different substrates with the aim to finely tune the lattice mismatch between SrTiO3 and the substrate material and the strain within the film. For SrTiO3 films grown on a DyScO3 substrate the particular value of the lattice parameters mismatch (~ 1 %) induces a tensile strain which shifts the ferroelectric transition close to the room temperature. The actual values of the temperature and strain then define the working point for example for the field-induced tuning of the low-frequency dielectric properties of the ferroelectric film, which may then find applications e.g. in THz or microwave modulators, tunable photonic crystals or metamaterials.
In the vicinity of a phase transition, ferroelectric materials are characterized by a fine compensation of various microscopic forces. Then, anharmonic properties of the crystalline lattice potential often play a crucial role and the material exhibits a strong nonlinear behavior. This opens a large potential for a number of tunable applications of such materials, e.g., by means of an external low-frequency electric field. 
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