Pyroelectricity

From Academic Kids

Pyroelectricity is the electrical potential created in certain materials when they are heated. As a result of a change in temperature, positive and negative charges move to opposite ends through migration, 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. The pyroelectric effect is also present in both bone and tendon. It is named from the Greek pyr, fire, and electricity.

Pyroelectric charge in minerals develops on the opposite faces of asymmetric crystals. The direction in which the propagation of the charge tends toward is usually constant throughout a pyroelectric material, but in some materials this direction can be changed by a nearby electric field. These materials are said to exhibit ferroelectricity. All pyroelectric materials are also piezoelectric, the two properties being closely related.

Very small changes in temperature produce pyroelectric charge. Motion detection devices are often designed around pyroelectric materials, as the heat of a human or animal from several feet away is enough to generate a difference in charge.

Progress has been made in creating artificial pyroelectric materials, usually in the form of a thin film, out of gallium nitride (GaN), cæsium nitrate (CsNO3), polyvinyl fluorides, derivatives of phenylpyrazine, and cobalt phthalocyanine. (See pyroelectric crystals.) Lithium tantalate (LiTaO3) is a crystal exhibiting both piezoelectric and pyroelectric properties which has been used to create small-scale nuclear fusion. [1] (http://www.nature.com/nature/journal/v434/n7037/suppinfo/nature03575.html)

The first reference to the pyroelectric effect is in writings by Theophrastus in 314 BC, who noted that tourmaline becomes charged when heated. Sir David Brewster gave the effect the name it has today in 1824. Both William Thomson in 1878 and Voight in 1897 helped develop a theory for the processes behind pyroelectricity. Pierre Curie and his brother, Jacques Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity. Pyroelectricity is definitely not a new concept, but research and application of the useful property continues to this day.

See also

de:Pyroelektrizität nl:pyro-elektrisch effect sv:Pyroelektricitet

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