Coexistence of the soft mode and sub-THz central peak in ferroelectric BaTiO3/(Ba,Sr)TiO3 superlattices

•BaTiO3/Ba0.3Sr0.7TiO3 superlattice was grown on a (0 0 1)MgO substrate.•Raman spectra of this superlattice were studied in the range 80–420 K.•The coexistence of the soft and the central mode was revealed in sub-THz region.•Emergence of the central mode explains dielectric properties of these superlattices.

Near- and sub-Terahertz dynamics of soft and Debye-type central modes was studied by the polarized Raman spectroscopy in ferroelectric BaTiO3/Ba0.3Sr0.7TiO3 (BT/BST) superlattice in the temperature range of 80–400 K where system undergoes the series of phase transitions: paraelectric-tetragonal–monoclinic in BT layers and paraelectric-orthorhombic-monoclinic in BST layers. It was shown that temperature evolution of these modes can be described within the model of coexisted damped harmonic oscillator and Debye relaxator. The occurrence of the pronounced central mode can explain the recently observed relaxor-like dielectric anomaly in such superlattice.