Phase transformations in barium-strontium niobate SBN-50 in the temperature range from 80 K to 700 K according to Raman spectroscopy data

The lattice dynamics of the Sr$_{0.5}$Ba$_{0.5}$Nb$_2$O$_6$ (SBN-50) ceramic was studied using Raman spectroscopy in the temperature range of 80-700 K with a step of 10 K. The analysis of the Raman spectra in the range $\nu$ = 50–1000 cm$^{-1}$ revealed features in the temperature dependence behavior of the optical modes frequencies associated with the displacement of Ba, Sr and Nb atoms from their average positions in the crystal lattice, which is associated with a macroscopic phase transition from the paraelectric to the ferroelectric phase in the vicinity of 390 K. It is shown that anomalies at $T\sim$ 565 K on the temperature dependences of the frequency and line half-width corresponding to the oscillations of the NbO$_6$ octahedron can be caused by the presence of polar nanoregions in the paraelectric phase in SBN-50. When the sample was cooled to a temperature of 80 K, the behavior was recorded in the Raman spectra, indicating the occurrence of a structural phase transition in the ferroelectric phase in the vicinity of 190 K. The reasons for the revealed patterns are discussed.