There is a very interesting kind of crystal, when you squeeze or stretch it, its two ends will produce different charges. This effect is called piezoelectric effect. The crystal that can produce piezoelectric effect is called piezoelectric crystal. Crystal（ α- Quartz is a famous piezoelectric crystal. Common piezoelectric crystals include: sphalerite, borax, tourmaline, marmatite, GaAs, barium titanate and its derivative crystal, KH2PO4, nakc4h4o6 · 4H2O (rosin salt), sugar, etc.

Piezoelectric crystal is an electronic material whose consumption is only next to monocrystalline silicon. It is used to manufacture electronic components for frequency selection and control. It is widely used in various fields of electronic information industry, such as color TV, air conditioner, computer, DVD, wireless communication, etc., especially in high-performance electronic equipment and digital equipment.   low corrosion tunnel density piezoelectric crystal is a necessary material for the production of SMD frequency chip and mobile phone frequency chip. Piezoelectric crystal products mainly include: Z-Bar, y-bar, thickness slice and frequency slice.

Piezoelectric effect of crystal

In some crystals, when the external force is applied along a certain direction, the internal polarization phenomenon will occur, causing the relative displacement of charged particles, thus generating charges of equal size and opposite sign on the crystal surface; When the external force is removed, it returns to the neutral state. The amount of charge produced by the force on the crystal is proportional to the size of the external force. This phenomenon is called piezoelectric effect. On the contrary, if the electric field is applied to the crystal, the crystal will produce mechanical deformation in a certain direction; When the applied electric field is removed, the deformation disappears. This phenomenon is called inverse piezoelectric effect, also called electrostrictive effect.

Principle of piezoelectric effect

The reason of piezoelectricity is related to crystal structure. When the center of gravity of the positive and negative charges are pressed, they are separated and form electric dipoles, so that the two ends of the crystal in a specific direction have different charges.

The common characteristic of piezoelectric crystal is that the crystal point group (symmetric type) has no symmetry center.

Among the 32 point groups, 21 point groups have no symmetry center, but the crystal of point group 432 has no piezoelectricity, so 20 point groups have piezoelectricity.