Dielectric constant polarization types in solids formula examples and applications
Before understanding the dielectric properties of solids, you need to have a clear understanding of what dielectric materials are and their characteristics. So, first we are discussing dielectric materials here in brief before explaining dielectric properties of solids.
About Dielectric Materials and Their Characteristics
An electrical insulator that can be polarized by an applied electric field is called dielectric or dielectric material. When materials which are conductors of electricity are placed under an electric field then electric charge or electrons flow through them. While when a dielectric is placed under an electric field, no electric charges flow through them. This is the reason they are called insulators. But these dielectric insulators under applied an electric field show polarization. It means when we apply an electric field on dielectric materials then electrons and positively charged nucleus of their atoms slightly shift from their average equilibrium positions. Due to this polarization in dielectric materials under the electric field, positive charges are displaced in the direction of the electric field while negative charges are displaced in the opposite direction to the electric field. It means the nucleus (positively charged) gets polarized towards the direction of the electric field while electrons get polarized in the opposite direction of the applied electric field.
For example, if the applied electric field is moving in the positive x – axis, then negative charges or electrons will shift in the negative x – axis. This polarization in dielectric material due to the electric field creates an internal electric field that reduces the overall field within the dielectric itself. When dielectric material is made up of weakly bonded molecules then these molecules not only get polarized on applying electric field but also reorient themselves so that their symmetry axes align to the field. This polarization of charges in dielectric materials results in the formation of dipoles. These dipoles in atoms or molecules of dielectric materials can arrange themselves in a systematic manner so that they will possess a net dipole moment, or they can arrange themselves in a way so that the net dipole moment will be zero. Although there are conditions in which dielectric materials possess no dipole in the crystal and only ions are present. Dielectric materials are important for explaining electronics, optics, solid – state physics and cell biophysics.
Dielectric Properties of Solids
The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Some dielectric properties of solids are as follows –
Piezoelectricity
Pyroelectricity
Ferroelectricity
Anti – ferroelectricity
Piezoelectricity
The solids in which individual dipoles are formed and align themselves in an ordered manner in such a way so that a net dipole moment of the solid (crystal) shows piezoelectricity. When pressure is applied in such solids, their atoms or ions are displaced and produce electricity. Piezoelectricity is an electric charge which accumulates in some crystals due to mechanical stress. It means piezoelectricity is electricity resulting from pressure and latent heat. The word piezoelectricity is derived from the Greek word piezein which means ‘to squeeze or press’ and elecktron, which means ‘amber’(an ancient source of electric charge). Piezoelectricity was discovered by French Physicists Jacques and Pierre Curie in 1880.
This dielectric property of solids is used in the medical field, automotive industry, information technology and telecommunications.
Pyroelectricity
The word ‘Pyroelectricity’ is derived from the two Greek words pyr which means ‘fire’ and elecktron which means ‘amber’(an ancient source of electric charge) or ‘electricity’. Pyroelectricity is the ability of certain crystals to produce a temporary voltage when they are heated or cooled. Some piezoelectric crystals produce electricity on heating, thus produced electricity is called pyroelectricity and this phenomenon is called pyroelectric effect. Pyroelectric crystals are generally naturally electrically polarized and as a result contain large electric fields. Due to change in temperature, positions of the atoms change within a crystal structure. Now due to change in crystal structure, polarization of the crystal changes which causes rise to a voltage across the crystal. Now if the temperature remains constant at its new value, the pyroelectric voltage disappears due to leakage current.
They are used in heat sensors, power generation and nuclear fusion. They can be used in PIR (passive infrared) sensors, infrared non – contact thermometers and motion detector thermal sensors. Motion detectors and thermal sensors are used to detect the movement of human beings, animals, and objects etc.
Ferroelectricity
In some crystals the dipoles are permanently aligned even in absence of electric field. They possess spontaneous electric polarization. On application of an external electric field on such crystals their electrical polarization gets reversed. It was discovered by Valasek in Rochelle salt in 1920. The word ferroelectricity is made up of two words ferro which means iron and electricity. All ferroelectric materials are pyroelectric as well.
It is used in ferroelectric capacitors, ferroelectric RAM, high quality infrared cameras, fire sensors, sonar, vibration sensors and fuel injectors on diesel engines. It is also used in ferroelectric tunnel junctions (FTJ). Ferroelectrics show catalytic properties. So, they can be used for catalysis as well. They can also act as energy harvesters. Materials which possess both ferroelectric and ferromagnetic properties are called multiferroics. Many researches are going on in multiferroics.
Anti – Ferroelectricity
As the name suggests it is opposite to ferroelectricity. The relation between anti - ferroelectricity and ferroelectricity is analogous to the relation of ferromagnetism and anti – ferromagnetism. Crystals which possess anti – ferromagnetism property consist of an ordered array of electric dipoles but with adjacent dipoles oriented in opposite (antiparallel) directions. This results in a net zero dipole moment. They possess zero spontaneous electric polarization since the adjacent dipoles cancel each other. This property of crystal can appear or disappear depending on temperature, pressure, growth method and external electric field etc. The temperature at which anti – ferroelectricity disappears is called Neel point or Curie point.
It is used in supercapacitors, integration with ferromagnetic materials, high energy storage devices etc.
Overview of Dielectric Properties of Solids
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FAQs on Dielectric Properties Of Solids And Their Polarization Mechanism
1. What are dielectric properties of solids?
The dielectric properties of solids describe how a solid material responds to an applied electric field by becoming polarized and storing electrical energy. These properties mainly include:
- Dielectric constant (relative permittivity, εr) – ability to store electrical energy.
- Dielectric polarization – alignment of charges or dipoles in an electric field.
- Dielectric loss – energy dissipated as heat.
They are important in understanding insulating materials, capacitors, ceramics, and solid-state electronic devices.
2. What is dielectric constant in solids?
The dielectric constant (εr) of a solid is the ratio of its permittivity to the permittivity of free space, defined as εr = ε / ε0. It indicates how much electrical energy the material can store compared to vacuum.
- ε = permittivity of the material
- ε0 = permittivity of free space (8.854 × 10-12 C2 N-1 m-2)
A higher εr means better energy storage capability, which is crucial for capacitor dielectrics.
3. What are the types of polarization in dielectric solids?
The main types of polarization in dielectric solids are electronic, ionic, orientation, and space charge polarization. These include:
- Electronic polarization – displacement of electron cloud relative to nucleus.
- Ionic polarization – relative displacement of positive and negative ions.
- Orientation polarization – alignment of permanent dipoles.
- Space charge polarization – accumulation of charges at grain boundaries or defects.
Each type contributes differently depending on the frequency of the applied electric field.
4. How does temperature affect the dielectric constant of solids?
The dielectric constant of polar solids generally decreases with increasing temperature because thermal motion disrupts dipole alignment. Specifically:
- In polar dielectrics, orientation polarization decreases at high temperature.
- In non-polar dielectrics, temperature has little effect.
In some materials like ferroelectrics, εr changes sharply near the Curie temperature.
5. What is dielectric loss in solids?
The dielectric loss of a solid is the energy dissipated as heat when it is subjected to an alternating electric field. It occurs because polarization cannot follow rapid field changes perfectly.
- Measured using loss tangent (tan δ).
- Higher dielectric loss means more energy wasted.
Low dielectric loss materials are preferred for high-frequency electronic applications.
6. What is the difference between polar and non-polar dielectrics?
The main difference between polar and non-polar dielectrics is the presence of permanent dipole moments in polar materials.
- Polar dielectrics (e.g., H2O in solid form) have permanent dipoles and show orientation polarization.
- Non-polar dielectrics (e.g., polyethylene) have no permanent dipoles and show mainly electronic polarization.
Polar dielectrics are more temperature-dependent than non-polar dielectrics.
7. What is the relation between dielectric constant and capacitance?
The capacitance of a capacitor filled with a dielectric solid is given by C = εr ε0 A / d, showing that capacitance is directly proportional to the dielectric constant.
- A = plate area
- d = separation between plates
- εr = dielectric constant
Thus, inserting a solid dielectric increases capacitance by a factor of εr.
8. What is ferroelectricity in solids?
The ferroelectricity of a solid is the property of having spontaneous electric polarization that can be reversed by an external electric field. These materials:
- Exhibit a hysteresis loop in polarization vs electric field.
- Have a characteristic Curie temperature.
Examples include BaTiO3 and PbTiO3, widely used in capacitors and memory devices.
9. How does frequency affect dielectric polarization in solids?
The effect of frequency on dielectric polarization is that different polarization mechanisms operate at different frequency ranges. Specifically:
- At low frequency, all types (electronic, ionic, orientation, space charge) contribute.
- At high frequency, only electronic polarization remains active.
As frequency increases, the overall dielectric constant usually decreases.
10. Why are dielectric solids important in chemistry and materials science?
Dielectric solids are important because they act as electrical insulators and energy storage materials in electronic and chemical applications. Their significance includes:
- Use in capacitors and solid-state devices.
- Role in understanding bonding and molecular polarity.
- Applications in ceramics, polymers, and semiconductor technology.
Studying dielectric properties helps in designing materials with controlled electrical behavior.
