Polarization & Types

The displacement of charged particles under the action of the applied
electric field is identified as dielectric polarization.
It occurs due to several microscopic mechanisms.
If the d.c  electric field is applied to a dielectric, the dielectric
polarization will set up in the dielectric. This polarization gives rise to
polarization vector

The polarization vector is created by four types of polarization
mechanisms.

1.Electronic polarization

Electronic polarization occurs due to the displacement of the positively charged nucleus and the negatively charged electrons of an atom in the opposite directions when an electric field is applied. The dipole moment-μ due to electronic polarization is proportional to the applied electrical field strength(E).It the dipole moment due to electronic polarization., E applied electric field and is called the electronic polarize ability. Electronic polarization is independent of temperature. Electronic polarization is takes place in almost all dielectric Electronic polarization sets in very quickly because it involves the displacement of lighter electron cloud. It also disappears quickly after the electric field is switched off.

2.Ionic polarization

Ionic polarization is due to the displacement of the positively and negatively
charged ions in the ionic crystal in the opposite directions when the electric filed
is applied.
Example, when electric field is applied to ionic crystals like NaCl and KCl-ionic
polarization sets in. Ionic polarization is independent of temperature. Ionic polarization sets in slowly as it involved the movement of ions which are relatively heavier. It is the dipole moment due to ionic polarization, is the ionic polarize ability and E is the applied electric field. 

3.Orientation polarization

Orientation polarization occurs in liquids or solids – which possess molecules with permanent dipole moment (i.e., in polar dielectrics). The orientation of these molecules will be random normally due to thermal agitation. Because of the randomness in orientation, the material has net zero dipole moment. But under the influence of an applied electric field, each of the dipoles undergo rotation so as to reorient along the direction of the field because of which, the overall cancellation of dipole moments due to randomness does not hold good any more. Thus the material acquires electrical polarization. Orientation polarization depends strongly on the temperature. Orientation polarization takes more time to set than ionic polarization. Orientation polarization where is dipole moment due to orientation polarization, Orientation polarize ability , and applied electric field E.

4.Space charge polarization.

Space charge polarization occurs due to the accumulation of charges at
the interfaces in multiphase dielectrics. It occurs in ferrites and semiconductors. The value of space charge polarization is very small compared to other types of polarizations. The space charge polarization is not an important factor in most dielectrics .