Features of the Electric Properties of Polar Solids

In all dielectrics, the action of an electrical field causes polarization described by the dielectric permittivity, which is a second rank tensor. Its components can differ significantly and also depend on the boundary conditions, in which the polar crystal is polarized: whether it is free or clamped, short-circuited or open-circuited, whether the polarization process is isothermal or adiabatic. In the isotropic dielectrics, the permittivity is scalar and does not depend on the listed conditions. Piezoelectric polar crystals are capable of generating polarization, which is proportional to the applied mechanical stress. This property is described by piezoelectric modulus, which is the material tensor of the third rank. The direct and converse piezoelectric effect can be described by four piezoelectric modules in dependence of boundary conditions. Electrostriction is a quadratic electromechanical effect characteristic of all dielectrics. This effect is usually small, so in the polar crystals it is not visible against the background of a stronger piezoelectric effect. Pyroelectric polar crystals are capable of generating a thermally induced polarization while the pyroelectric coefficient is a first rank material tensor. Pyroelectric, unlike a piezoelectric, can serve as a sensor of change in hydrostatic pressure which is used in liquid media. The electrocaloric effect is opposite to the pyroelectric effect and consists in the changing of temperature of pyroelectric crystal when the electric field is applied to it. The coefficient of the electrocaloric effect is proportional to the pyroelectric coefficient. This effect may have applications in microelectronics as solid cooling devices which use antiferroelectrics in the vicinity of their electrically induced phase transition.