RAMAN SCATTERING BY POLARITONS IN TETRAGONAL BATIO3

Raman scattering spectra by polaritons of A1 symmetry in tetragonal BaTiO3 at room temperature are used to establish the q ≈ 0 TO phonon frequencies and to estimate the dielectric constant along the ferroelectric axis ε{lunate}cs. Values of ε{lunate}cs = 37 ± 5 and ε{lunate}cs = 38 ± 6 are found from the LST relation and the polariton dispersion curves respectively. It is also found that the two broad bands centered at 270 cm-1 and 520 cm-1 correspond to TO phonons. Their widths are explained by large anharmonic couplings and a frequency dependent damping constant. © 1969.