Influence of anisotropic strain on the dielectric and ferroelectric properties of SrTiO₃ thin films on DyScO₃ substrates

The in-plane dielectric and ferroelectric properties of coherent anisotropically strained SrTiO₃ thin films grown on orthorhombic (101) DyScO₃ substrates were examined as a function of the angle between the applied electric field and the principal directions of the substrate. The dielectric permittivity revealed two distinct maxima as a function of temperature along the [100]_p and [010]_p SrTiO₃ pseudocubic directions. These data, in conjunction with optical second-harmonic generation, show that the switchable ferroelectric polarization develops first predominantly along the in-plane axis with the larger tensile strain before developing a polarization component along the perpendicular direction with smaller strain as well, leading to domain twinning at the lower temperature. Finally, weak signatures in the dielectric and second-harmonic generation response were detected at the SrTiO₃ tilt transition close to 165 K. These studies indicate that anisotropic biaxial strain can lead to new ferroelectric domain reorientation transitions that are not observed in isotropically strained films.