Piezoelectricity or, literally, pressure electricity, is an unusual property exhibited by a few ceramic materials: an electric polarization — the alignment of electric dipoles in a common direction, which gives rise to an electric field that is oriented in this same direction — is induced in the ceramic crystal when a mechanical strain (dimensional change) is imposed on it. The inverse piezoelectric effect is also displayed by this group of materials; that is, a mechanical strain results from the imposition of an electrical field.
This property is characteristic of materials having complicated crystal structures with a low degree of symmetry. Natural piezoelectric materials include Quartz, Tourmaline, Rochelle Salt, Langasite. Synthetic piezoelectric materials include barium titanate (BaTiO3), lead titanate (PbTiO3), lead zirconate–titanate (PZT) [Pb(Zr, Ti)O3], and potassium niobate (KNbO3). The piezoelectric behaviour of a polycrystalline specimen may be improved by heating above its Curie temperature and then cooling to room temperature in a strong electric field (pooling process). Piezoelectric materials are utilized in transducers, which are devices that convert electrical energy into mechanical strains, or vice versa.
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