Views:0 Author:Site Editor Publish Time: 2019-10-10 Origin:Site
Piezoelectric ceramic is a polycrystalline film with piezoelectric effect, and its production process is named after its similar production process (raw material pulverization, molding, high temperature sintering). Some anisotropic piezo crystals undergo deformation under mechanical force, causing the charged particles to be relatively displaced,PZT material piezo ceramic disc is resulting in positive and negative bound charges on the surface of the piezo crystal. This phenomenon is called piezoelectric effect. This property of the crystal is called piezoelectricity. Piezoelectricity was discovered in 1880 by J. Curie and P. Curie brothers. A few months later they experimentally verified the inverse piezoelectric effect, that is, when a voltage is applied to the piezo crystal, the piezo crystal will undergo geometric deformation. Before 1940, only two types of ferroelectrics were known (not only spontaneously polarized in a certain temperature range, but also the spontaneous polarization of the crystals that can be reoriented due to the external field strength): one is the rest salt and some closely related tartrate; one is potassium dihydrogen phosphate and its equivalent. The former has piezoelectricity at normal temperature, and has technical use value, but has the disadvantage of being easy to dissolve; the latter has piezoelectricity at low temperature (less than -14 C), and the engineering use value is not large. Barium titanate (BaTiO) was found to have an abnormally high dielectric constant between 1942 and 1945. It was soon found to be piezoelectric, and the discovery of BaTi O piezoelectric ceramics was a quantum leap in piezoelectric materials. Previously, there was only a piezoelectric single crystal material, and thereafter a piezoelectric polycrystalline material, piezoelectric ceramic appeared and was widely used. In 1947, the United States used BaTiO ceramics to make pickups for phonographs. Japan used it two years later than the United States. BaTiO has the disadvantage that the piezoelectricity is weaker than the resting salt and the piezoelectricity is larger than the piezo quartz crystal with temperature. In 1954, B. Jaffe and others discovered the piezoelectric PbZrO-PbTiO (PZT) solid solution system, which is an epoch-making event that made it impossible to fabricate devices in the BaTiO era. Since then, PZT transparent piezoelectric ceramics have been developed to extend the application of piezoelectric ceramics to the field of optics. So far, the application of piezoelectric ceramics, from the development of the universe to the life of the family, is extremely extensive. China's research on piezoelectric ceramics began in the late 1950s, about 10 years later than foreign countries. At present, there are quite strong forces in the trial production and industrial production of piezoelectric ceramics. Many materials have reached or are close to the international level.
The physical mechanism of piezoceramic piezoelectricity
Piezoelectric ceramics are polycrystals whose piezoelectricity can be explained by the piezoelectricity of the piezoelectric discs crystal. Under the action of mechanical force, the total electric dipole moment (polarization) changes, resulting in a piezoelectric phenomenon. Piezoelectricity is closely related to polarization, deformation.
Microscopic mechanism of polarization
The polarization state is a state in which the electric field exerts a relative displacement force on the charged point of the dielectric and a temporary balance of mutual attraction between the charges. There are three main polarization mechanisms.
(1) Electron displacement polarization—The atom or ion of a dielectric does not coincide with the negative charge center of a positively charged nucleus and a shell electron under the action of an electric field force.
(2) Iong displacement polarization—the positive and negative ions of the dielectric are relatively displaced under the action of an electric field force, thereby generating an electric dipole moment.
(3) Orientation polarization—the polar molecules that make up the dielectric have a certain intrinsic (inherent) electric moment. Due to thermal motion, the orientation is disordered, the total electric moment is zero. When an electric field is applied, The direction of the electric field is aligned and a macroscopic electric dipole moment appears.
For anisotropic crystals, the relationship between polarization and electric field
2. Piezoelectric effect
(1) Positive piezoelectric effect
When the peizoelectric discs ceramic transducer is deformed by an external force, the positive and negative charge centers are relatively displaced, and the opposite charges are generated on some corresponding faces, and the polarization intensity occurs. This phenomenon of no electric field and polarization by deformation is called a positive piezoelectric effect.
For anisotropic crystals, stress is applied to the piezo crystal, and the crystal will exhibit a proportional polarization in the three directions of X, Y, and Z, which are called piezoelectric stress constant and piezoelectric strain constant, respectively.
(2) Inverse piezoelectric effect
When an electric field is applied to the crystal, not only polarization but also deformation is generated, and this phenomenon of deformation by the electric field is called an inverse piezoelectric effect. This is because when the crystal is subjected to an electric field, stress (piezoelectric stress) is generated inside the crystal, and piezoelectric strain is generated by stress.
3. Mechanism of pressure effect
The piezoelectric effect was first discovered on piezo crystals. Now we use PZT material crystals as a model to illustrate the physical mechanism of the piezoelectric effect.
When no pressure is applied, the positive and negative charge centers of the piezo crystal are distributed. At this time, the positive and negative charge centers coincide, and the total electric moment of the piezo crystal is equal to zero, and the crystal surface is not charged (not piezoelectric).
When pressure sensor is applied in the x direction, the material crystal is deformed, and the positive and negative charge centers are separated, that is, the electric dipole changes, so that charge accumulation occurs on the X plane.
When pressure is applied in the Y-axis direction, the distribution of the positive and negative charge centers of the crystal is shown here, when the total electric dipole moment changes and causes a charge accumulation on the X plane opposite to the front. Obviously, it is replacing the previous compressive force with a tensile force indicates that the sign of the charge is reversed. In short, when a pressure sensor is applied to a piezoelectric crystal, a piezoelectric effect may be caused.