Ion jump polarization

Displacements that occur between several equilibrium sites for which the probability of occupancy of each site depends on the strength of the external field. This mechanism is also known as dipolar or ion jump polarization and is depicted schematically in Fig. 14.10. Another definition of ion jump polarization is the preferential occupation of equivalent or near-equivalent lattice sites as a result of the applied field biasing one site with respect to the other. If the alignment occurs spontaneously and cooperatively, nonlinear polarization results and the material is termed ferroelectric. Because of the relatively large displacements, relative dielectric constants on the order of 5000 can be attained in these materials. Nonlinear dielectrics are dealt with separately in Chap. 15. But if the polarization is simply due to the motion of ions from one adjacent site to another, the polarization behavior is linear with voltage. These solids are discussed below. 

As noted above, ion jump polarization is the preferential occupation of equivalent or near-equivalent lattice sites as a result of the applied fields biasing one site over the other. The situation is depicted schematically in Fig. 14.10, where an ion is localized in a deep energy well, but within which two equivalent sites, labeled A and B in Fig. 14.106, exist. The sites are separated from each other by a distance A, and an energy barrier In the absence of an electric field (Fig. 14.10fl), each site has an equal probability of being occupied and there is no net polarization. In the presence of a field (Fig. 14.106) the two sites are no longer equivalent — the electric field will bias the B sites, resulting in a net polarization. 

Assuming ion jump polarization is responsible for the variation in tan0, estimate both tq and A//, [defined in Eq. (14.56)]. 

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