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Ferroelectric phase transition in tensile-stressed SrTiO3 thin films and heterostructures

Theoretically predicted ferroelectric phase induced by tensile stress was confirmed in SrTiO3 epitaxial films and SrTiO3/DyScO3 heterostructures on DyScO3 substrates, prepared in top world laboratories. It occurs near 270 K and it is drive by a soft phonon mode in the THz range which couples to a low-frequency overdamped excitation (at ~ 10 cm–1) in the whole measured temperature range of 20-300 K. The soft mode is strongly tunable by the electric field which results in a tunable permittivity of such heterostructures up to the THz range, attractive for applications. We proposed a general model of the soft-mode behavior in strained SrTiO3 films applicable in a wide range of temperatures and applied fields.

For details see
C. Kadlec et al., J. Phys.: Condens. Matter 21, 115902 (2009),
C. Kadlec et al., Phys. Rev. B 80, 174116 (2009),
D. Nuzhnyy et al., Appl. Phys. Lett. 95, 232902 (2010),
V. Skoromets et al., J. Appl. Phys. 107, 124116 (2010).

Temperature dependence of polar mode frequencies and high-frequency permittivity in SrTiO3 thin films on DyScO3 substrate as evaluated from the IR reflection and THz transmission spectra and from microwave resonance measurements. The film thicknesses are listed in the figure.

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