# The Properties Of Dielectric Materials

866 Words 4 Pages
1.1 Dielectric Materials
Dielectric materials are insulating materials that exhibit the property of electrical polarization. Dielectric materials support charge by acquiring a polarisation in an electric field.
1.1.1 Electric susceptibility and permittivity
When a capacitor with capacitance C0 is filled with a dielectric material, its charge storage capacity (capacitance) increases to a value of C. Than susceptibility (χ^') of the dielectric materials is given by

χ^'= (C-C_0)/C

Dielectric permittivity〖 (ε〗_r) is defined as the ratio of the capacitance C of the capacitor filled with a dielectric to the value C0 of the same capacitor under vacuum and given as ε_r= C/C_0 =>χ^'= ε_r-1
1.1.2 Polarization
The polarization P is defined as
When electric field is applied, it causes the electron cloud to distort in one direction while the nucleus moves in the other direction. Since the center of electron cloud no longer coincides with the nucleus, a dipole moment develops.

Ionic polarisation
To undergo ionic polarisation, a material must have an ionic structure i.e. it must be composed of cations and anions. This ion pair (cation and anion) already possesses a dipole moment before the application of an electric field, however the sum of dipole moments over the entire material (i.e. net polarization) may still be zero. When electric field is applied it causes the ionic bond to stretch. If the material possessed a spontaneous polarisation before the application of the field, this will cause it to increase by increasing the magnitude of the individual dipole moments. When field in opposite direction is applied, this field causes compression of the bond and thus decreases the dipole moment. For group of ions the distortion of bonds caused by the electric fields leads to an off-centering of the cations with respect to the anions (and vice

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