Ferroelectric superlattice based on barium–strontium titanate solid solutions

A superlattice of the composition Ba$_{0.8}$Sr$_{0.2}$TiO$_3$/Ba$_{0.4}$Sr$_{0.6}$TiO$_3$ has been grown by rf cathode sputtering on a MgO(001) substrate. The unit cell parameters of the superlattice layers along the normal to the substrate, modulation period, and orientation relationships between the film and the substrate have been determined using X-ray diffraction. Based on the temperature dependences of the polarized Raman spectra, it has been revealed that the frequency of soft mode E(TO) increases from 79 to 97 cm$^{-1}$ in the temperature range of 80–350 K. It has been found that there are no characteristic indications of a sequence of phase transitions, which take place in bulk samples of barium–strontium titanate solid solutions of identical compositions, and the transition from the ferroelectric to paraelectric phase in the superlattice occurs at a temperature of $\sim$ 350 K.