Relaxor ferroelectricity in strained epitaxial $SrTiO3$ thin films on $DyScO3$ substrates

The ferroelectric properties of $500Å$ thick strained, epitaxial $SrTiO3$ films grown on $DyScO3$ substrates by reactive molecular-beam epitaxy are reported. Despite the near 1% biaxial tensile strain, the x-ray rocking curve full widths at half maximum in $ω$ are as narrow as $7arcsec$ (0.002°). The films show a frequency-dependent permittivity maximum near $250K$ that is well fit by the Vogel-Fulcher equation. A clear polarization hysteresis is observed below the permittivity maximum, with an in-plane remanent polarization of $10μC∕cm2$ at $77K$⁠. The high $Tmax$ is consistent with the biaxial tensile strain state, while the superimposed relaxor behavior is likely due to defects.