This document presents information about dielectric materials. It begins with an introduction that defines dielectrics as insulating materials that can store and release electrical energy and discusses their role in applications like capacitors. It then defines dielectrics as materials that do not conduct electricity easily and have high resistivity. The document goes on to discuss different types of polarization that can occur in dielectrics, including electronic, ionic, orientation, and space charge polarization. It also covers related topics such as dielectric constant, polarizability, and electric susceptibility.

1. DIELCTRIC
MATERIALS
PRESENTED BY:
VARUNAPRIYA.K
22ECR225

2. INTRODUCTION
• Dielectrics are insulating materials that can store and release electrical energy.
• They play a crucial role in various applications, such as capacitors and
electrical insulation.
• This presentation will explore the properties and behavior of dielectrics,
providing a comprehensive understanding of their importance in electrical
systems.

3. DEFINITION OF DIELECTRICS
• A dielectric is a material that does not conduct electricity easily, exhibiting
high electrical resistance.
• The resistivity of dielectric material is around 10^10 to 10^20 ohm meter.
• Dielectric materials function as insulators and it is chiefly used as a storage
medium for electrical charge
• The forbidden energy gap between the valence band and conduction band
of the dielectric material is very huge under normal circumstaneus

4. DIELECTRIC CONSTANT
• The dielectric constant of any substance refers to the relative permittivity of the dielectric
substance .
• It is the proportion of the permittivity of the material to the permittivity of the free space.
• Mathematically it can be expressed as :
k = ϵ/ϵ0
Where ,
ϵ refers to the permittivity of the substance
ϵ0 refers to the permittivity of the free space

5. ELECTRIC POLARIZATION AND
POLARISIBILITY
• The process of producing electric dipoles by an electric field is called
polarization in dielectrics..
• The induced dipole moment per unit electric field is called as polarisibility .
The induced dipole moment is proportional to the intensity of the electric
field
• μ∝E
μ= α E
α -> polarisibility constant

6. ELECTRIC SUSEPTIBILITY
• The electric susceptibility is generally defined as the constant of
proportionality related to an Electric Field E to the induced dielectric
polarisation density P. Electric susceptibility is also known as dielectric
susceptibility..
• xₑ = P/E.
• In the meter-kilogram-second system, electric susceptibility is defined slightly
differently because the constant permittivity of a vaccum ε₀, gets included
here. The expression comes out something like this
• xₑ = P/(ε₀E).

7. VARIOUS TYPES OF POLARIZATION
• When the specimen is placed inside a DC electric field ,
polarization can be classified into four types of process
• 1. Electronic polarization
• 2. Ionic polarization
• 3.Orientation polarization
• 4. Space charge polarization

8. ELECTRONIC POLARIZATION
• Electronic polarization is the redistribution of electrons in a molecule or
material in response to an external electric field. In other words, when an
electric field is applied, the negatively charged electrons within a material or
molecule shift slightly in one direction, causing a temporary separation of
charges and the creation of a dipole moment.
• Electronic polarization plays a crucial role in the behavior of materials such
as ferroelectric and piezoelectric materials, which have important
technological applications in fields such as data storage and sensing. It is also
important in the behavior of molecules in chemical reactions and in the
properties of materials used in electronic devices.
•

9. IONIC POLARIZATION
• Ionic polarization occurs in ionic materials. It occurs when an electric field is applied
to an ionic material then cations and anions get displaced in opposite directions
giving rise to a net dipole moment. ..Example : Polyatomic gases
• In absence of electric field E, the distance between the ions is d but in presence of
electric field, distance between the ions increases..The dipole moment p for each ion
pair is equal to the product of charge on each ion and relative displacement…..That
is p = qd
• Thus ionic polarization is given as….Pe =n αiE
• where αi is constant of proportionality known as ionic polarizability constant.
• This polarization is independent of temperature.

10. ORIENATION POLARIZATION
• Orientational polarization is observed in the materials having a covalent
bond of ionic character and molecules having a partial ionic bond.
• The existence of a permanent moment is purely a matter of molecular
geometry. Two hypothetical cases are shown in the figure below. The
molecules are of the form ABA. B atom i is negatively charged, whereas
A’s are positively charged. The arrangements of the figure give a net-zero
dipole moment in the absence of the field, whereas the molecular
geometry of the figure gives a resultant dipole moment in the absence of
the field. CO2 is an example of the first case and NO2, and H2O are
examples of the second case.

11. The permanent dipole moment has been denoted as Pp, and the presence of an electric field
will tend to align Pp along its own direction since E exerts a torque on Pp. The contribution of
this process of the orientation of the permanent dipoles in the direction the field contributed
additionally to total polarization and is called the orientational polarisation denotes as P0.

12. •For moderate fields and all but very low temperatures, the
orientational polarization P0 may be given by,
• P0= Npp2E/3kT
•For the above expression orientational polarizability α0 is defined aa
• α0= pp2/3kT
here N, Pp, and E are defined previously, k is Boltzmann’s constant, and
T is temp[erature is kelvin.
•Orientational polarizability is a function of temperature and it
decreases as temperature increases.

13. SPACE CHARGE POLARIZATION
• Space charge polarization is also known as interfacial polarization.
It is observed in multiphase materials. materials with defects are
known as multiphase materials.
• Space charge polarization arises due to the accumulation of charge
in lattice vacancies of material. these charges will induce image
charges and thus generate +ve and -ve charge centers separated by
a small distance which results in a dipole moment. These dipole
moments give rise to a polarization known as space charge or
interfacial polarization.

15. TOTAL POLARIZATION:
The total polarization of a multiphase material containing
permanent dipoles is given by,
P=Pe+Pi+P0+Ps
For a single-phase dielectric containing permanent dipoles,
P=Pe+Pi+P0
P =N(αe+αi)E+3kTNpp2E

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