Pyroelectric, piezoelectric, flexoelectric, and thermal polarization effects in ionic crystals

An analysis has been made of the linear response of polarization to a uniform change in temperature, in its gradient (thermal polarization effect), in macroscopic deformation and in its gradient (flexoelectric effect). It has been shown how the use of some definitions of polarization widespread in the literature can lead to essentially incorrect results in the analysis of piezo- and flexoelectric effects in the field of elastic deformations of an acoustic wave. It has also been shown that in calculating the above responses in the case of a spatially uniform disturbance in a sample of finite size two classes of contributions arise: 1) contributions depending on the microscopic properties of the lattice, and 2) contributions depending only on changes in the distortion tensor accompanying the response, and on multipole moments of the charge distribution of the whole unperturbed crystal. In this connection it was established that the former contributions are bulk effects while the latter ones are surface or false contributions (which are not manifested in the generally accepted experimental arrangements for measurements). The special features of the manifestation of the flexoelectric and thermal polarization effects are discussed in detail.