An Introduction
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
1. What are the properties of dielectric materials?
Dielectric materials are poor conductors of electricity. That is if any dielectric material is placed in an electric field, there will be no conduction of electricity through that material. There are 4 types of dielectric properties for solid dielectric materials. Those are piezoelectricity, pyroelectricity, ferroelectricity, and antiferroelectricity.
2. What is a perfect dielectric material?
The perfect dielectric material is a material with zero electrical conductivity. That means no electricity will flow if kept in an electric field. Dielectric materials only exhibit displacement current and hence It will store electrical energy just like the capacitor does. An example of perfect dielectric material is dry air. Dry air is an excellent perfect dielectric material as it is used in the construction of capacitors and even in types of transmission lines.
3. What is the difference between insulator and dielectric?
Dielectric Material is where there is poor conduction of electricity. An insulator is a material that does not allow any current to pass through it. Through interpretation of meaning, the insulator and dielectric material might seem the same. But the major difference between the dielectric material and insulator is that the insulator opposes the flow of electrons and dielectric material stores the electric energy. The dielectric materials can be polarized whereas insulators cannot be polarized.
4. Is water a dielectric material?
The dielectric material is a material that is a poor conductor of electricity. Liquid Water is not and dielectric material as water is not an electrical insulator. Moreover, water is difficult to use as a capacitor as it is not pure enough to conduct electricity. When a graph is plotted between C versus frequency, Water possesses nonlinear characteristics. Which makes water a poor dielectric material to be used in capacitors.
5. What is the use of dielectric materials?
The dielectric material is a material that can be polarized and has little electrical conductivity. Dielectric materials are used in many electrical components such as capacitors. Capacitors are used to store electrical energy, and dielectric materials have the ability to store electrical energy. Another major area where dielectric materials are used is the wires, insulating materials, cables, and sensor devices.
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