The impact of strain on structure and ferroelectric properties of epitaxial SrTiO3 films on various substrate materials—substrates with larger (DyScO3) and smaller (NdGaO3 and CeO2/Al2O3) in-plane lattice constant, respectively—was analyzed. In all cases, (001)-oriented strained epitaxial SrTiO3 was obtained. It is demonstrated that the mismatch of the lattices or, alternatively, the mismatch of the thermal expansion coefficients of films and substrate, imposes biaxial strain on the SrTiO3 films. The strain leads to a small tetragonal distortion of the SrTiO3 lattice and has a large impact on the ferroelectric properties of the films. With decreasing film thickness and at low temperatures the permittivity deviates from the “classical” Curie-Weiss behavior. Furthermore, strain-induced ferroelectricity is observed, which agrees with theoretical predictions. For electric fields parallel to the film, surface-induced ferroelectricity is observed for SrTiO3 that is exposed to in-plane tensile strain, i.e., SrTiO3 on DyScO3 and sapphire. Transition temperatures of To≈210 K and To≈325 K are obtained for SrTiO3 on CeO2/Al2O3 and DyScO3, respectively. [ABSTRACT FROM AUTHOR]
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