Piezoelectricity is the property of various materials to either generate an electricity when mechanical stress is applied. These materials can also function by doing the opposite, they can generate mechanical power when voltage is applied. Until mechanical stress or electrical power is applied to the material it remains overall electrically neutral.

Piezoelectric materials can generate astounding amounts of voltage. For instance, if you properly apply mechanical stress to a 1 cm cube of quartz with 2 kN (500 lbf) of correctly applied force can produce a voltage of 12,500 V.

The piezoelectric property commonly is found in materials with a crystalline structure. This is because the structure of the crystal contains positive and negative electrical charges; each separated from the next but placed at symmetric locations throughout the crystal. Each side of the crystal structure forms an electric dipole. Dipoles are pairs of equal and oppositely charged or poles separated by a distance. When dipoles are near each other they tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but can be aligned during a process by which a strong electric field is applied across the material. This process is called poling. Poling is usually at elevated temperatures. There is also a process called poling that is referred to when polarizing permanent magnets but the only relation that the two terms have is the meaning that they are creating polarities of some sort within a material.Spatially separated charges result in an electric field. This means that in a piezoelectric material there will always be an electric potential.

Some commonly used piezoelectric materials are listed bellow. All of these are either naturally occurring or man-made.
  • cane sugar
  • quartz
  • berlinite
  • Rochelle salt
  • topaz
  • tourmaline
  • Dry bone
  • Tendon
  • Silk
  • Wood due to piezoelectric texture
  • Enamel
  • Dentin
  • gallium orthophosphate (GaPO4)
  • Langasite (La3Ga5SiO14)
  • Man-made ceramics
  • Tetragonal unit cell of lead titanate
  • barium titanate (BaTiO3)
  • lead titanate (PbTiO3)
  • lead zirconate titanate (Pb[ZrxTi1-x]O3 0<x<1)
  • potassium niobate (KNbO3)
  • lithium niobate (LiNbO3)
  • lithium tantalate (LiTaO3)
  • sodium tungstate (Na2WO3)
  • Ba2NaNb5O5
  • Pb2KNb5O15
  • Polyvinylidene fluoride (PVDF)
  • Lead-free piezoceramics
  • Bismuth ferrite (BiFeO3)

Application of piezoelectric materials:

Electric cigarette lighters, gas grill and stove igniters use piezoelectric piezoelectric crystal to ignite a flammable gas. When you press a button a hammer to hits a chunk of some sore of piezoelectric. This generates a high enough voltage to allow electric current to jump across a small spark gap. This heats and ignites the gas.

Photo by Anthony
Piezoelectrics are also commonly used for detecting sound such as in piezoelectric microphones. When sound waves hit the material it distorts and produces an electric signal. The term transducer is sometimes used when the device both sends and detects mechanical force. This is usually used in ultrasonic sensors which emit a sound and then detect the vibration when it bounces off a surface.

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