Journal of the American Ceramic Society, Vol.102, No.5, 2791-2799, 2019
Phonon behaviors and dielectric functions in Bi0.5Na0.5TiO3-based ceramics by Raman scattering and optical ellipsometry
The dielectric functions and lattice vibrations of (0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO(3)-xSrTiO(3) (BNBSTx) ceramics were investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Based on the analysis of dielectric functions with the Tauc-Lorentz dispersion model, it was found that the band gap and the temperature coefficient increased with the addition of SrTiO3. Moreover, the frequency, intensity and/or full width at half maximum of phonon modes related to Bi and Ti-localized phonon modes exhibited local maximum/minimum around the depolarization temperature and permittivity-maximum temperature, which indicated the ongoing structural transformation. In addition, the Sr introduction affected the TiO6 tilting and the off-center displacement of Ti4+. These results seem to be significant for the enhanced response functions with the addition of SrTiO3 in BNBSTx ceramics.