Properties of the low-frequency phonon spectra of ferroelectric barium titanate-based heterostructures

Polarized Raman spectra of the epitaxial Ba0.5Sr0.5TiO3 film, bi-color BaTiO3/Ba0.5Sr0.5TiO3 superlattice, and tri-color BaTiO3/Ba0.5Sr0.5TiO3/SrTiO3 superlattice were studied in a broad temperature range of 80-700 K. Based on the temperature dependence of the polar modes we determined the phase transitions temperatures in the studied heterostructures. In the sub-THz frequency range of the Y(XZ)Y spectra, we revealed the coexistence of the Debye-type central peak and soft mode in bi-color BaTiO3/Ba0.5Sr0.5TiO3 superlattice.