Pyroelectric Crystals and their Applications

PYROELECTRIC CRYSTALS AND THEIR APPLICATIONS

(i) The pyroelectric materials such as BaTiO₃, LiNibo₃, etc are used to make very good infra-red detectors which can operate at room temperature.

(ii)Materials such as TGS, Triglycine sulphate NaNO2 and Jode of PZT, lead zirconate titanate ceramics are used in the Quae construction of pyroelectric image tubes.

Ferroelectric energy convertor

It is a device which converts heat energy into electrical energy based on pyro-electric effect.

Principle

The ferroelectric crystals exhibit the phenomenon of pyroelectric effect, i.e., change in the temperature of the crystal produces a change in its polarisation.

Using this effect, one can convert heat energy into useful electrical energy.

Description

Ferroelectric crystal BaTiO₃ is placed in between two parallel plate capacitors C₁and C₂ as shown in fig 1.36 (a).

The capacitor and the crystal can be charged with the help of an external battery.

Initially, the temperature of the system is kept at T₁ K (just below the ferroelectric curie temperature ' θ ') and the capacitor is charged to a voltage V₁.

Initial energy (E₁) = C₁ V₁²  = area of the triangle abc fig

(b) where C¹ is the capacitance of the capacitor at T₁ K.

Now, the capacitor is separated from the circuit and it is heated upto temperature T₂. Due to heating, the dielectric constant ε_r decreases and the capacitance also decreases.

Now, when the capacitor is charged for the same value of charge as it in temperature T, it is found that the voltage starts increasing from V₁ to V₂.

 Increase in energy E₂ =  ½ C₂ V₂²

 Net increase in energy

∆  E = E₂ - E₁

=1/2 ( C₂V₂² – C₁ V₁² )

This increase in heat energy can be converted into electric power by discharging the capacitor through the bond resistor R₁