Raman spectroscopic study of Na1/2Bi1/2TiO3-x%BaTiO3 single crystals as a function of temperature and composition

A Raman spectroscopic study of Na1/2Bi1/2TiO3-x%BaTiO3 (NBT-x%BT) single crystals with x = 0 and 5.6 has been performed as a function of temperature from 25 to 600 °C. The general features of the Raman spectra for the various compositions were similar over the region of the phase diagram investigated, with only subtle changes between rhombohedral (R), tetragonal (T) and cubic phases. The peaks were broad, with no significant narrowing on cooling through a phase transition. We find evidence of an oxygen octahedral rotational mode in the paraelectric state. On cooling near and below the ferroelectric Curie temperature, a gradual change in intensity of the A-O and B-O peaks occurred with decreasing temperature. Evidence of a ferroelectric → antiferroelectric transition was found near 200–250 °C, consistent with the onset of dispersion in the dielectric constant. The phase transition mechanism was discussed. The findings indicate the presence of a broad distribution of quasistatic local structural distortions...