Dispersion of the oblique phonons in tetragonal BaTiO3 and Ce: BaTiO3

Raman spectra of oblique phonons in tetragonal BaTiO3 and Ce : BaTiO3 single crystals were obtained for different values of the angle θ which the phonon wavenumber q̄ makes with the c‐axis. On the basis of Merten's equation, the directional dispersion curves were fitted and plotted. The results show that the A1(TO) phonons of BaTiO3 at 275 and 514 cm−1 come from first‐order scattering, which is evidence for the order—disorder model of the ferroelectric phase transition. The Raman spectra of Ce : BaTiO3 are reported for the first time and the results indicate that Ce atoms have little effect on the structure of BaTiO3.