Coupled acoustic modes in tetragonal BaTiO3: temperature dependence

The acoustic velocities in BaTiO3 were measured as a function of temperature up to 350°C by means of Brillouin scattering. The behavior of the transverse acoustic phonons propagating along [001], so called coupled phonon, in tetragonal BaTiO3 was discussed in relation to that of the spontaneous polarization on the basis of the piezoelectric equation. The scattering intensity of the coupled phonon mode is related to an effective photoelastic constant including the electro-optic coefficient through the piezoelectric interaction.