Polarization diffusion and dielectric friction

Relaxation of nonequilibrium polarization fields in dielectrics is usually theoretically treated solely in terms of the reorientational motion of the polar molecules. If, however, the translational diffusion of these molecules is also taken into account, dielectric relaxation is accelerated. This results in the lowering of the dielectric friction that retards the motion of an ion or dipole in a dielectric. This reduction in dielectric friction is here calculated for two models: a time-dependent dipole at the center of a sphere, and a moving charge on the axis of a cylinder, each immersed in a dielectric. A parameter measuring the relative importance of rotation and diffusion is identified, and a substantial lowering of the dielectric friction is implied in many situations. It is shown that the boundary conditions play a decisive role in the properties of the fields. Directions for a further development of the theory of polarization diffusion are indicated.