Polarization rotation transitions in anisotropically strained SrTi O ₃ thin films

Commensurately strained epitaxial SrTi O3 thin films on a GdSc O3 substrate with anisotropic in-plane tensile strains of 1.46% and 1.59% were grown. By using optical second harmonic generation and polarization measurements, a ferroelectric transition from a tetragonal 4mmm phase to a ferroelectric mm2 phase at ∼400 K and an antiferrodistortive transition to a multiferroic phase at 150-175 K are observed, which are in agreement with thermodynamic calculations. In addition, a series of polarization rotation transitions between 〈100〉p to 〈l00〉p (0<l<1) is observed in the 4-400 K temperature range.