Macroscopic quadrupole moment of dielectric solids with structural phase transitions

The macroscopic quadrupole moment is the main electronic characteristic of structural transformations between nonpolar states of dielectric solids. Several experimental methods are suggested for measuring the different components of the quadrupole moment tensor as a function of external actions. We describe the observation of quadrupole pyro-and piezoelectric, inverse piezoelectric, and electrooptic effects in centrosymmetric crystals without phase transitions, some quadrupole effects in the regions of ferroelastic and nonferroelastic phase transitions, and effects arising due to plastic deformation. The influence of defects on the quadrupole moment of real crystals is considered. Special attention is paid to the observation and study of the anomalously large quadrupole effects related to a frozen polarization wave in incommensurate phases of ferroelectrics. The experimental and theoretical data published up to 1984 are reviewed and some new results are presented.