Advanced Solid State Physics

Figure 127: Dependence of the dielectric constant of the temperature and the voltage

14.3.2 Polarizability

There are different sources of polarizability. Four of them are discussed in this chapter:

• Electronic polarizability


• Ionic polarizability


• Orientation polarizability


• Space charge polarizability

Electronic polarizability:

We think of an atom. There we have the positive protons somewhere in the middle and the negative
electrons are moving around the protons. The resulting dipole moment is zero. If an electric field is
applied, the protons and electrons will move in opposite directions and so a dipole moment is induced.
Of course, if the applied field is oscillating, the generated dipoles will oscillate too.

For gases the polarization is easy to describe mathematically. It’s just proportional to the electric
field and the count of atoms with the polarizationαas constant of proportionality:

P=NαE=Np (248)

In solids and liquids the local field depends on the applied field and the field induced by the neighboring
dipoles. There are three types of fields to observe. The applied field, the local microscopic field around
the atom and the macroscopic field, which is the mean electric field over many atoms, but smaller