Ionic polarization is polarization caused by relative displacements between positive and negative ions in ionic crystals.

Ionic polarization occurs, when atoms form molecules and it is mainly due to a relative displacement of the atomic components of the molecule in the presence of an electric field.

When a field is applied to the molecule, the positive ions displaced by X1 to the negative side of electric field and negative ions displaced by X2 to the positive side of field.

The resultant dipole moment-

$\mu= e (X_1+X_2 )$.....(1)

Restoring force $F=αx$ or $F=βx$… $β$ is restoring force constant Restoring force constant depend upon the mass of the ion *m* and natural frequency $ω_0$ and is given by $F=mω_0^2 x$,,,,,(a) We know,$F=eE$.....(b) Let, $F=Kx_1$.....for positive ion $F=Ix_2$.....for negative ion *Here K and I are restoring force constants and F is a restoring force* $K=mω_0^2 x_1$ $I=mω_0^2 x_2$ *Where 'M'* *mass of a negative ion and* *is mass of positive ion* From (a) and (b) $x= \dfrac{eE}{mw_0^2 }$ $\therefore x_1=\left(\dfrac {eE}{w_0^2 }\right)\left(\dfrac{1}{m}\right)$ & $x_2=\left(\dfrac{eE}{w_0^2}\right)\left(\dfrac{1}{M}\right)$ $\therefore x_1+x_2=\left(\dfrac{e}{w_0^2 }\right)\left(\dfrac{1}{m}+\dfrac{1}{M}\right)$.....(2) Substituting (2) in (1), we get $\mu_i = \dfrac{e^2E}{w_0^2 }\left(\dfrac{1}{m}+\dfrac{1}{M}\right)$ $α_i=\dfrac{μ_i}{E}$ $\therefore α_i=\dfrac{e^2}{w_0^2}\left(\dfrac{1}{m}+\dfrac{1}{M}\right)$

This polarization occurs at frequency 1013 Hz (Infrared region).

It is a slower process compared to electronic polarization but is independent of temperature.