Paraelectric, piezoelectric and pyroelectric crystals: I. Dielectric properties

The dielectric properties of crystals are studied on the basis of the weakly anharmonic crystal model. Particular emphasis is placed on the low frequency behaviour of the dielectric susceptibility and on the possibility of a coupling between the dielectric properties and the fluctuations in the phonon density distribution. These fluctuations cannot be treated by low-order perturbation theory but can be discussed by solving the appropriate transport equation. The approximate solution to this equation is obtained following the techniques developed for ultrasonic attenuation.