Homoepitaxial Sr1+xTiO3+δ films with -0.2 ≤ x ≤ 0.25 grown by reactive molecular-beam epitaxy on SrTiO3 (001) substrates have been studied by ultraviolet Raman spectroscopy. Non-stoichiometry for strontium- deficient compositions leads to the appearance of strong first-order Raman scattering at low temperatures, which decreases with increasing temperature and disappears at about 350 K. This indicates the appearance of a spontaneous polarization with a paraelectric-to-ferroelectric transition temperature above room temperature. Strontium-rich samples also show a strong first-order Raman signal, but the peaks are significantly broader and exhibit a less pronounced temperature dependence, indicating a stronger contribution of the disorder- activated mechanism in Raman scattering.
Tenne, Dmitri A. and Farrar, A. K.. (2010). "Ferroelectricity in Non-Stoichiometric SrTiO3 Films Studied by Ultraviolet Raman Spectroscopy". Applied Physics Letters, 97(14), 142901-1 - 142901-3. http://dx.doi.org/10.1063/1.3499273