Piezoelectric materials          

Piezoelectricity i.e. electricity from pressure was discovered by Pierre and Jacque Curie more than 100 years ago. Piezoelectric materials are materials that physically deform in the presence of an electric field, or conversely, produce an electrical charge when mechanically deformed. This effect is due to the spontaneous separation of charge within certain crystals structures producing an electrical dipole. Generation of charge on mechanical stress was first observed in the crystals of zinc blende, sodium chlorate, borocite, tourmaline, quartz calamine, topaz, tartaric acid, cane sugar and Rochelle salt etc.. At present, polycrystalline ceramics are the most common class of piezoelectric materials. Polycrystalline ceramics are composed of randomly oriented minute crystallites. Each crystallite is further divided into tiny ‘domains’ or regions having similar dipole arrangements. Initially the polar domains are oriented randomly showing little macroscopic piezoelectric behavior. During manufacturing, the material is subjected to a large electrical field [of the order of 2kV/mm] at a temperature above the Curie temperature which orients the polar domains in the direction of the external electrical field. It results in material exhibiting macroscopic piezoelectric behavior [Figure 11.1].

Figure 11.1: Polarization (poling) of a piezoelectric ceramic