pyroelectrics

Pyroelectrics are materials that exhibit a change in spontaneous polarization in response to a change in temperature. The temperature-induced variation in polarization generates electric charge on the material’s surface, which can be collected as a current or voltage when the temperature is modulated. The pyroelectric effect is quantified by the pyroelectric coefficient p = dP/dT, with instantaneous current i = p A dT/dt and charge Q = p A ΔT for a plate of area A undergoing a temperature change ΔT.

Characteristics of pyroelectric materials include lacking a center of symmetry and possessing a permanent polarization. In many cases this polarization arises because the material is ferroelectric at room temperature; heating through a Curie temperature removes ferroelectric order and the spontaneous polarization, diminishing the pyroelectric response. Some materials that are not ferroelectric can still be pyroelectric due to their crystal structure.

Common pyroelectrics encompass natural crystals such as tourmaline and quartz, synthetic ferroelectric crystals like lithium niobate and lithium tantalate, and pyroelectric polymers such as polyvinylidene fluoride (PVDF) and related copolymers.

Applications of pyroelectrics include infrared detectors and cameras, flame detectors, motion sensors, and pyroelectric energy harvesting devices that convert thermal cycling into electrical energy. Performance depends on crystal orientation, thickness, electrode interface, and the rate of temperature change; noise and drift can limit sensitivity. Devices often employ differential or differential-sampling techniques to improve signal-to-noise and stability.