The 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 ${\text{SrTiO}}_{3}$ thin films grown on orthorhombic (101) ${\text{DyScO}}_{3}$ 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 ${[010]}_{p}$ ${\text{SrTiO}}_{3}$ 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 ${\text{SrTiO}}_{3}$ 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.