Temperature Dependence of Dispersion Relation of Over-Damped E- Polariton in BaTiO3

The temperature dependence of the dispersion relation of the over-damped E-polariton in BaTiO 3 is presented. The low-frequency dielectric constant ε a has been obtained from the slope of the polariton dispersion relation. From the best fit of the spectra, both the quasi-harmonic frequency of E-phonon ω 0 and its damping constant γ were determined. The values of the dielectric constant ε a were compared to those obtained from the capacitance measurements. The discrepancy of the temperature dependence of the dielectric constants in several frequency regions suggests that there is a dielectric dispersion of the relaxation type around a few hundred MHz.