Engineering the ferroelectric and resistivity Properties of Oxide Films via Compressive and Tensile Strain

Strain can strongly modify the electronic characteristics of oxide materials. For instance the phase transition from the ferroelectric to the dielectric state can be shifted by up to 300 K in either directions. As a result, room temperature permittivity can be enhanced significantly, e.g. for SrTiO3 from εRT≈600 to εRT≈25000. Moreover the resulting ferroelectrics are highly anisotropic and show a number of properties that are extremely interesting for various applications. In this work we try to perform a systematic study of the impact of strain on the system BaxSr(1-x)TiO3. Films with different stoichiometric and thickness are epitaxially grown on DyScO3, TbScO3 and GdScO3 substrates. The lattice mismatch between substrate and film leads to different in-plane compressive and tensile strain within -1.5% to 1.5% in these systems. Tensile strain causes an increase of the in-plane ferroelectric dielectric phase transition temperature, while compressive strain decreases the transition temperature. The films show a metal-insulator transition and an extremely large tunability, they represent relaxor-type ferroelectrics and the ferroelectric properties are highly anisotropic. The data are discussed in terms of existing model for relaxor-type ferroelectrics. The potential of these films for sensors (e.g. surface or bulk acoustic wave devices) is examined