Piezoelectricity, also called the piezoelectric effect, is the property of some crystalline materials to polarize generating a voltage when they are subject to mechanical deformation (direct piezoelectric effect) and at the same time to deform in an elastic way when subjected to a voltage (reverse piezoelectric effect or Lippmann effect); the sign of polarization reverses depending on whether the deformation is due to compression or traction.

Which means that there is a coupling between the electrical and the mechanical state of the material. When a piece of piezoelectric material is mechanically deformed, e.g. compressed, a current will flow and charge its faces. and vice versa, it will be deformed when exerted to an electrical field.

This piezoelectric effect occurs only along a certain direction and the deformations associated with it are of the order of a nanometer.

There are many materials that exhibit piezoelectric properties such as quartz, topaz, polymers, sucrose, silk, Rochelle salt, PVDF, and many ceramics. But why don’t all materials exhibit this property? The reason for that is that for piezoelectricity to appear, the material must be crystalline but not have a symmetry center.

So piezoelectricity is a characteristic property of any crystal without a center of symmetry. In fact, all the bodies that crystallize in one of the 21 crystallographic classes without a center of symmetry (with one exception) have more or less marked piezoelectricity.

History and discoveries

The discovery of the piezoelectric effect dates back to 1880 by Pierre Curie and Paul-Jacques Curie who first discovered the direct piezoelectric effect in quartz and later, following the hypothesis of Gabriel Lippmann, they discovered the inverse piezoelectric effect.

Piezoelectricity applications

From the point of view of the crystalline structure, piezoelectric materials normally have various geometric configurations equivalent from the point of view of energy, that is, of the stability of the system, but oriented differently.

The electric polarization of the piezoelectric material follows the mechanical action (and vice versa) with a very short delay of the order of 10–8 s, and the virtually instantaneous response makes the piezoelectric crystals particularly suitable as high fidelity electromechanical and electroacoustic transducers (accelerometers, microphones, etc.).

Piezoelectricity is primarily used as input for certain components such as actuators, sensors, and oscillators. It is used to detect voltages, sound waves, electronic frequency, pressure, and mechanical movements. The aforementioned components use the electric charge generated from a piezoelectric material for certain processes or functions.

Piezoelectric crystals can also be used for the generation and reception of ultrasonic oscillations, as well as high selectivity resonators and electric oscillators; also piezoceramics, polycrystalline ceramic materials characterized by a high piezoelectric coefficient, are increasingly used in the realization of miniaturized engines (such as those used in cameras) and electromechanical actuators (needles selectors in frames, valves control, etc.).

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