Dielectric dispersion in tetragonal BaTiO₃ measured by double-axis brillouin spectroscopy

Abstract

The dispersion of the dielectric constant ϵ_a of the tetragonal BaTiO₃ was determined at room temperature from Brillouin scattering data of the TA phonons propagating along the [101] direction. The dielectric constant ϵ_a was obtained by measuring the shift of the velocity of the TA phonon due to its piezoelectric coupling to the overdamped soft TO phonon of E-symmetry. The resultant values of ϵ_a are consistent with earlier data, and the dispersion of ϵ_a above 10⁷ Hz was found to be well described by a one oscillator a dielectric function due mainly to the soft TO phonons. The appropriate value of the truly static dielectric constant ϵ_a was determined to be 2100.