Pyroelectricity

PYROELECTRICITY

Pyroelectric effect is the change in spontaneous polarization when the temperature of the specimen is changed. The pyroelectric coefficient λ  is defined as the change in polarization specimen.

λ = dP / dT

The change in polarization results in change in external field and hence charge on the surface. As it is possible to detect a charge of 10^-16 C with a suitable electrometer, temperature changes as small as 10^-6°C can be measured using the pyroelectric effect.

The barium titanate crystal in figure 1.35 is also said to be pyroelectric because when the temperature increases, the crystal expands and the relative distances of ions change. The Ti⁴⁺ ion becomes shifted, which results in a change in the polarization.

Temperature changes = δ T

The heat absorbed by the crystal increases the temperature by δ T, which induces a change  δ P in the polarization. This is the pyroelectric effect. The change δ P gives rise to a change δ V the voltage that can be measured.

(Examples: Barium Titanate, Lithium Niobate, Lithium Tantalate and Polyvinyl fluoride).