On the Method of Fluctuation Background for the Investigation of Acoustic Properties of Ferroelectrics

The effect of polarization fluctuations on the behaviour of acoustic properties of ferroelectrics at second-order phase transition is investigated using the general principles of thermodynamics of irreversible processes. The obtained equations bring out the physical sense of the absorption mechanism: the elastic wave induces polarization, and an essential role in the formation of the electromechanical coupling is played by spatially-heterogeneous polarization fluctuations. There exists a linear relationship between polarization and elastic stress even in the absence of a piezoelectric effect. This mechanism is essential only close to the Curie point. The sound wave propagation, absorption and internal friction coefficients are obtained. The results are in agreement with available experimental data.