pyroelectric

Pyroelectricity is the electric polarization that changes in response to temperature variations in certain crystalline materials. When the temperature is changed, the spontaneous polarization of the crystal shifts, causing surface charges to appear. If the crystal is left electrically connected, a current flows; if the circuit is open, a voltage develops across the crystal. The pyroelectric coefficient, p, quantifies the rate of change of polarization with temperature (dP/dT).

Pyroelectricity occurs only in crystals that lack a center of symmetry and possess a polar axis. It is closely related to ferroelectricity: all ferroelectric materials are pyroelectric, but not all pyroelectric materials are ferroelectric or have switchable polarization.

Common pyroelectric materials include natural tourmaline and synthetic crystals such as lithium niobate (LiNbO3) and lithium tantalate (LiTaO3); zinc oxide (ZnO); and ferroelectric ceramics like lead zirconate titanate (PZT) near its Curie temperature. Pyroelectricity is also observed in polymers such as polyvinylidene fluoride (PVDF). The magnitude of the pyroelectric coefficient varies among materials, typically ranging from 10^-4 to 10^-8 coulombs per square meter per kelvin, depending on composition and temperature.

Applications focus on detectors and energy conversion. Pyroelectric materials are used in infrared detectors and thermal imaging cameras, as well as in motion and flame detectors. They are also explored for converting heat fluctuations into electrical energy in energy-harvesting devices, and for various microelectronic and optical applications.

History and context: the pyroelectric effect was identified in the 19th century by the Curie brothers, establishing a foundation for subsequent research in ferroelectric and sensor technologies.