# What is Pyroelectric Material : Mathematical Analysis & Its Applications

A dielectric material is an electrical insulator, which has the capacity of stopping the flow of current through it. They are classified into Centro symmetric materials and piezoelectric materials, further piezoelectric is classified as non-pyroelectrics and pyroelectrics, pyro electrics are further classified as non-ferroelectrics and ferroelectrics. This article specifies pyroelectric material. It was discovered in the early 20th century by a Greek scientist. The name pyroelectricity is derived from Greek where pyro means fire and electricity. It is a general property of certain crystal which are polarised to obtain large electric field. These pyroelectric materials are hard in nature and crystalline.

## What is Pyroelectric Material?

Pyroelectricity or pyroelectric material is an electric response of polar dielectric with a change in temperature. If the temperature in return changes it causes the movement of atoms from there neutral position hence the polarization of the material changes, we observe a voltage across the material. This effect is temporary now suppose the temperature remains constant at its new value. The pyroelectric voltage becomes zero due to the leakage current. So, within this same temperature limits, the charges developed by the effect of heating or cooling are equal and opposite.

Pyroelectric materials exhibit spontaneous polarization that is polarization in the absence of electric field, this cannot be changed or reversed on applying the electric field it does so in ferroelectric materials. Hence all pyro electro materials are also piezoelectric. The piezoelectric materials have a certain kind of piezoelectric crystal that does not allow pyroelectricity. Hence pyroelectric effect takes place below the 1070-degree F curie temperature, so when the material is heated above curie temperature 1070-degree F the atoms come back to their equilibrium positions. So, the electrocaloric effect is considered as a physical inverse of the pyroelectric effect.

### List of Pyroelectric Materials

Some of the pyroelectric materials are listed below

• Tourmaline
• gallium nitride
• cesium nitrate (CsNO3)
• polyvinyl fluorides
• derivatives of phenyl pyridine
• cobalt phthalocyanine
• Lithium tantalite (LiTaO3).

### Comparison between Pyro Electricity and Thermo Electricity

The electrocaloric effect is the phenomenon in which the material shows the reversible temperature change on the applied electric field. Hence pyroelectricity is different from thermoelectricity. Pyro crystal changes temperature from one degree to another resulting in a temporary voltage across the crystal.

Whereas in the case of thermoelectricity the two ends of the device are subjected to two different temperatures resulting in a permanent voltage in the device resulting in as there is the temperature difference.

### Difference between Piezoelectric, Pyroelectric and Ferroelectric Materials

The following are the differences between Piezoelectric, Pyroelectric and Ferroelectric Materials

 Parameters Piezoelectric Pyroelectric Ferroelectric Function Piezoelectric materials generate electricity whenever mechanical stress is applied. Pyroelectric material generates electric potential whenever heated or cooled. Ferroelectric material exhibits electric polarization even in the absence of an electric field. Examples Quartz, crystal,Ammonium, Phosphate Quartz crystal, Ammonium, Phosphate. Lithium niobite, Barium Titanite Properties Non-centrosymmetric, Non-polar dielectric, Presence of Piezoelectric effect where P= dσ. They are unidirectional polarization, non-centrosymmetric, It exhibits pyroelectricity when T >= Tc They are easily polarized, They exhibit dielectric hysteresis, They are both pyro and piezoelectric in nature. Applications Acts like a transducer, Used in microphones, It generates ultrasonic waves. IR detectors, Image tubes, Temperature sensing elements. Ultrasonic transducers They are pressure transducer It acts as a memory device like a random access memory.

### Mathematical Analysis of Pyroelectric Material

A thin piece of a pyroelectric material is an electrode and connected to an amplifier which is of high impedance, a field-effect transistor (FET) as shown below. Let it be the pyroelectric current which generates voltage V across the electric admittance Ye. A voltage amplifier of unity gains couples the high impedance source of current to a low input impedance following the circuit. If p’ is a component of pyroelectric coefficient p the orthogonal to the electrode surface of area A. The generated current is independent of thickness since the current is associated with the unbounded surface charge.

Where,

Charge  Q = p’ A Δ T…….. 1

Pyroelectric current ip = Ap’dT/dt …….. 2

Pyroelectric voltage  V=i/УE ……… 3

Where electrical admittance УE = GA + GE + jw CA + CE …….4

Shunt and sample conductance GA, GE

Shunt and sample capacitance CA, CE

Equivalent capacitance of the dielectric is C = €σa/Ad                                   ……5

Stored energy E = ½ p2€σAhΔT2                    …….6

d = material thickness; €σ = permittivity constant at stress, A = Area of protection, p’ = component of pyroelectric coefficient p.

If an electric field E is applied to a material, the total dielectric displacement d that is a charge per unit area of the plate, on both the sides of a pyroelectric material is,

d= E s +€ E                                 ……….7

where € is the permittivity of vacuum and Es is spontaneous polarization of volume density of electric dipole moment.

#### Effect of Pyroelectric Coefficient with Temperature

From the above analysis, the pyroelectric coefficient has an effect of temperature

• Pyroelectric coefficient increases with an increase in temperature
•  It depends on the order of phase transition and is larger for second-order transitions
• Tc is a curie temperature where the pyroelectric material increases.

The advantages of pyroelectric materials are

• Pollution Free
• Maintenance cost is less
• Very high-frequency response

The disadvantage of pyroelectric materials is

• Require high impedance cable
• Static motions cannot be measured easily.

#### Applications

The applications of Pyroelectric materials are

• PIR – based motion detectors
• Solar energy pyroelectric converter
• Detection and protection of wildlife
• PIR remote-based thermometer
Fire detector
• Laser diagnostic.

### FAQs

##### 1). What are pyroelectric crystals?

The pyroelectric crystals are materials that produce electricity when the temperature of the crystal is increased.

##### 2). Are all ferroelectrics Piezo electrics?

Yes, all ferroelectrics Piezo electrics but not all piezoelectrics are ferroelectrics.

##### 3). Is quartz a pyroelectric?

Yes, quartz is a pyroelectric crystal.

##### 4). What is a pyro sensor?

The pyro sensor is also named as a pyro detector or thermal detector. Where if there is a small change in temperature charge is developed on the surface of the crystal which is the electric current required.

##### 5). Can crystals store data?

Yes, crystals can store data.

##### 6). Does the thermal background influence the pyroelectric effect?

No,  the thermal background does not influence the pyroelectric effect.

Thus, the pyroelectricity is a property of certain crystal which exhibits polarization, where an electric response is generated with the change in temperature. The pyroelectric effect takes place below the 1070-degree F that is curie temperature. They require high impedance cable for its operation which provides a good frequency response. Here is a question for you, what is the function of pyroelectric material?