Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled.
As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e. the material becomes polarised) and hence, an electrical potential is established.
Pyroelectricity can be visualized as one side of a triangle, where each corner represents energy states in the crystal: kinetic, electrical and thermal energy.
The side between electrical and thermal corners represents the pyroelectric effect and produces no kinetic energy.
The side between kinetic and electrical corners represents the piezoelectric effect and produces no heat.
Although artificial pyroelectric materials have been engineered, the effect was first discovered in minerals such as quartz and tourmaline and other ionic crystals.