Piezoelectric Effect

Piezoelectric Effect, appearance of an electric potential across certain faces of a crystal when it is subjected to mechanical pressure. Conversely, when an electric field is applied on certain faces of the crystal, the crystal undergoes mechanical distortion. Pierre Curie and his brother Jacques discovered the phenomenon in quartz and Rochelle salt in 1880 and named the effect piezoelectricity (from Greek piezein,”to press”).

The piezoelectric effect occurs in several crystalline substances, such as barium titanate and tourmaline. The effect is explained by the displacement of ions in crystals that have a nonsymmetrical unit cell, the simplest polyhedron that makes up the crystal structure (see Crystal). When the crystal is compressed, the ions in each unit cell are displaced, causing the electric polarization of the unit cell. Because of the regularity of crystalline structure, these effects accumulate, causing the appearance of an electric potential difference between certain faces of the crystal. When an external electric field is applied to the crystal, the ions in each unit cell are displaced by electrostatic forces, resulting in the mechanical deformation of the whole crystal. Because of their capacity to convert mechanical deformation into electric voltages, and electric voltages into mechanical motion, piezoelectric crystals are used in such devices as the transducer, record-playing pickup elements, and the microphone. Piezoelectric crystals are also used as resonators in electronic oscillators and high-frequency amplifiers, because the mechanical resonance frequency of adequately cut crystals is stable and well defined.