Can a tensile tensile strained TiO2 thin film be ferroelectric?

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A series of papers about discovery of new ferroelectrics using PFM microscopy has recently been published. On the example of strained TiO2 thin films, which exhibit ferroelectric-like hysteresis loops, we have shown that PFM response can originate in electrochemical effects like migration of defects in the  electric field. Additional experiments like temperature dependent second harmonic generation, IR spectroscopy of phonons and X-ray diffraction are always necessary for unambiguous confirmation of ferroelectric phase transitions.

Dielectric loss spectra of TiO2 thin film
Description
(a) Schema of anatase crystal structure of TiO2 under tensile strain.
(b) Dielectric loss spectra calculated from temperature-dependent reflectance spectra of 20 nm thin film of TiO2 reveal no temperature shifts of phonon frequencies, which does not support the ferroelectric phase transition even ifthe PFM studies detected hysteresis loops up to 460 K.

Contact person: Stanislav Kamba