Elastic strains in thin films and artificial superlattices composed of alternating layers of ferroelectric compounds provide a new route to enhance the properties of known ferroelectrics and create materials with superior properties for device applications. The series of ferroelectric BaTiO3/Ba1-xSrxTiO3 (BT/BST-x) superlattices deposited on (001)MgO substrate using a PLD technique. The structural parameters of the layers were determined by X-ray diffraction. Near- and sub-Terahertz dynamics of soft and Debye-type central modes was studied by the polarized Raman spectroscopy of the BT/BST-x superlattices in the temperature range of 80-500 K. Due to the stress gradients in these BT/BST-x superlattices the phase transitions in BT and BST-x layers occur at different temperatures and depend on chemical composition of the BST-x layers. It was shown that temperature evolution of the low-frequency Raman spectra can be described within the model of coexisting damped harmonic oscillator and Debye relaxator. The occurrence of the pronounced central mode can explain the recently observed relaxor-like dielectric anomalies in BT/BST-x superlattices. We demonstrate that variation of chemical composition of the BST-x layers allows to tune distortions in alternating layers and to modify the shape of the dielectric permittivity as a function of temperature.
We acknowledge financial support from the RSF (grant N 14-12-00258) and FP7-ITN-NOTEDEV.