Surface acoustic waves in ferroelectrics

We have considered the phase velocity dispersion of the Rayleigh waves on the surface of ferroelectric crystal and in a thin ferroelectric film deposited on a metal plate in the close vicinity of a structure phase transition. The drastic softening of the ferroelectric crystal elastic constants when its symmetry changes at the phase transition results in the critical slowdown of the Rayleigh waves. We have calculated temperature dependencies of the Rayleigh velocity and dispersion curves at some temperatures close to the critical value. As the temperature is cooled down to the critical value, the dispersion dependency of the surface acoustic wave velocity changed qualitatively its behavior. The effect can be used for investigations of the critical properties of various layered ferroelectric systems. In particular, it can be used for measurements of the critical temperatures of the structure phase transitions in ultrathin ferroelectric films with thicknesses less than 100 nm.