What is Dielectric Material – Properties & Its Applications

Materials are categorized as conductors, insulators and semiconductors based on their electrical conducting properties. Every material is made up of molecules which in turn made up of atoms. When subjected to electric field these atoms in the material undergoes certain displacements and changes in properties. In October 1745, an experiment done by Ewald Georg von Kleist of Germany by connecting a high-voltage electrostatic generator to a volume of water collected in a hand-held jar using a wire showed that charge can be stored. Using this phenomenon, Pieter van Musschenbroek invented the first capacitor called “Leyden Jar”. The new material property that backed this invention was “Dielectric”.

What is the Dielectric?

Every material is made up of atoms. Atoms contain both negatively and positively charged particles. The central nucleus of the atom is positively charged. In any material, the atoms are arranged as dipoles represented with a positive and negative charge on its end. When these materials are subjected to electric field dipole moment takes place.

A conductor material starts conducting when electricity is applied. An insulator opposes the flow of electricity as it does not have any free moving electrons in its structure. But Dielectric is a special type of insulator that does not conduct electricity but gets polarized when subjected to electricity.

In Dielectric materials, when subjected to the electric field the positive charges present in the material gets displaced in the direction of the applied electric field. The negative charges are shifted in the direction opposite to the applied electric field. This leads to Dielectric polarization. In dielectric material, electric charges do not flow through the material. Polarization reduces the overall field of the dielectric.

Properties of Dielectric

The term Dielectric was first introduced by William Whewell. It is the combination of two words- ‘Dia’ and ‘electric’. The electrical conductivity of a perfect dielectric is zero. A dielectric stores and dissipate the electrical energy similar to an ideal capacitor. Some of the main properties of a Dielectric material are Electric Susceptibility, Dielectric polarization, Dielectric dispersion, Dielectric relaxation, Tunability, etc…

Electric Susceptibility

How easily a dielectric material can be polarized when subjected to an electric field is measured by the electric susceptibility. This quantity also determines the electric permeability of the material.

Dielectric Polarization

An electric dipole moment is a measure of separation of negative and positive charge in the system. The relationship between the dipole moment (M) and the electric field (E) gives rise to the properties of dielectric. When the applied electric field is removed the atom return to its original state. This happens in an exponential decay manner. The time taken by the atom to reach its original state is known as Relaxation time.

Total Polarization

There are two factors that decide the polarization of dielectric. They are the formation of dipole moment and their orientation relative to the electric field. Based on the elementary dipole type there can be either electronic polarization or ionic polarization. Electronic polarization P_e occurs when the dielectric molecules forming the dipole moment are composed of neutral particles.

Ionic polarization P_i and electronic polarization both are independent of temperature. Permanent dipole moments are produced in the molecules when there is an asymmetrical distribution of charge between different atoms. In such cases, orientational polarization P_o is observed. If a free charge is present in the dielectric material it would lead to the Space charge polarization P_s. The total polarization of dielectric involves all these mechanisms. Thus the total polarization of the dielectric material is

P_Total = P_i + P_e + P_o + P_s

Dielectric Dispersion

When P is the maximum polarization attained by the dielectric, t_r is the relaxation time for a particular polarization process, the dielectric polarization process can be expressed as

P(t) = P[1-exp(-t/t_r )]

The relaxation time varies for different polarization processes. Electronic polarization is very rapid followed by ionic polarization. Orientation polarization is slower than ionic polarization. Space charge polarization is very slow.

Dielectric Breakdown

When higher electric fields are applied, the insulator starts conducting and behaves as a conductor. In such conditions, dielectric materials lose their dielectric properties. This phenomenon is known as Dielectric Breakdown. It is an irreversible process. This leads to the failure of dielectric materials.

Types of Dielectric Material

Dielectrics are categorized based on the type of molecule present in the material. There are two types of dielectrics – Polar dielectrics and Non-polar dielectrics.

Polar Dielectrics

In polar dielectrics, the center of mass of positive particles does not coincide with the center of mass of negative particles. Here the dipole moment exists. The molecules are asymmetrical in shape. When the electric field is applied the molecules align themselves with the electric field. When the electric field is removed random dipole moment is observed and the net dipole moment in the molecules becomes zero. Examples are H2O, CO2, etc…

Non-Polar Dielectrics

In the non-polar dielectrics, the center of mass of positive particles and negative particles coincide. There is no dipole moment in these molecules. These molecules are symmetrical in shape. Examples of non-polar dielectrics are H2, N2, O2, etc…

Examples of Dielectric Material

Dielectric materials can be solids, liquids, gases, and vacuum. Solid dielectrics are highly used in electrical engineering. Some examples of sold dielectrics are porcelain, ceramics, glass, paper, etc… Dry air, nitrogen, sulfur hexafluoride and the oxides of various metals are examples of gaseous dielectrics. Distilled water, transformer oil are common examples of liquid dielectrics.

Applications of Dielectric Material

Some of the applications of dielectrics are as follows-

• These are used for energy storage in capacitors.
• To enhance the performance of a semiconductor device, high permittivity dielectric materials are used.
• Dielectrics are used in Liquid Crystal Displays.
• Ceramic dielectric is used in Dielectric Resonator Oscillator.
• Barium Strontium Titanate thin films are dielectric which are used in microwave tunable devices providing high tunability and low leakage current.
• Parylene is used in industrial coatings acts as a barrier between the substrate and the external environment.
• In electrical transformers, mineral oils are used as a liquid dielectric and they assist in the cooling process.
• Castor oil is used in high-voltage capacitors to increase its capacitance value.
• Electrets, a specially processed dielectric material acts as electrostatic equivalent to magnets.

FAQs

1). What is the use of dielectric in capacitors?

Dielectrics used in the capacitor helps to decrease the electric field which in turn decreases the voltage thereby increasing the capacitance.

2). Which dielectric material is widely used in capacitors?

In capacitors, dielectric materials such as glass, ceramic, air, mica, paper, plastic film are widely used.

3). Which material has the highest dielectric strength?

A perfect vacuum is noted to have the highest dielectric strength.

4). Are all insulators are dielectrics?

No, although the dielectrics behave as insulators, not all insulators are dielectrics.

Thus, Dielectrics form an important part of capacitors. A good dielectric material should have good dielectric constant, dielectric strength, low loss factor, high-temperature stability, high storage stability, good frequency response and should be amendable to industrial processes. Dielectrics also play a vital role in high-frequency electronic circuits. Measurement of dielectric properties of material gives information about its electrical or magnetic characteristics. What is a dielectric constant?