Interaction of Acoustic Waves With Polarization Waves in Ferroelectrics

An expression for effective elastic constants which control the behavior of acoustic waves interacting with polarization waves in ferroelectrics is derived using the linear response theory. If interactions due to the piezoelectric effect only are taken into account, then the frequency and space dispersion of effective elastic constants are essentially determined by those of the linear dielectric susceptibility. Some consequences of this direct relation between the elastic and dielectric properties of ferroelectrics are discussed for the ultrasonic attenuation and the Brillouin or neutron scattering by acoustic waves.