Piezoelectric ceramic materials Material classification:
Inorganic piezoelectric material
Divided into piezoelectric crystals and piezoelectric ceramics, piezoelectric crystals generally refers to piezoelectric single crystals; piezoelectric ceramics refers to piezoelectric polycrystals. Piezoelectric ceramics are polycrystals in which fine crystal grains obtained by the solid-phase reaction and sintering processes between powders and particles are randomly mixed together by mixing, molding, and high-temperature sintering with raw materials of necessary ingredients.
Piezoelectric ceramics are called piezoelectric ceramics, and they are actually ferroelectric ceramics. There are ferroelectric domains in the grains of this ceramic. The ferroelectric domains consist of 180 domains with spontaneous polarization directions anti-parallel and 90 domains with spontaneous polarization directions perpendicular to each other.
These domains are artificially polarized (strongly applied. Under DC electric field conditions, the spontaneous polarization is fully aligned in the direction of the external electric field and maintains the residual polarization after the withdrawal of the external electric field, and therefore has macroscopic piezoelectricity. Such as barium titanate BT, lead zirconate titanate PZT, modified lead zirconate titanate, lead metaniobate, lead niobate lithium niobate PBLN, modified lead titanate lead titanate. The successful development of this type of material promoted acoustic transducers and piezoelectric transmission.
Sensor performance improvement and improvement of various piezoelectric devices.
Piezoelectric crystals generally refer to piezoelectric single crystals, which refer to crystals that grow in an orderly manner in the long-range crystal lattice. This crystal structure has no symmetry center and therefore has piezoelectricity. Such as crystal (quartz crystal), lithium niobate, lithium niobate, titanium niobate and iron transistor lithium niobate, lithium niobate and so on.
In contrast, piezoelectric ceramics have high piezoelectricity, high dielectric constant, and can be processed into arbitrary shapes, but they have the low mechanical quality factor, large electrical loss, and poor stability, and are therefore suitable for high-power transducers and wide-band filters. Applications, but not ideal for high frequency, high stability applications. Quartz and other piezoelectric single crystal piezoelectricity is weak, the dielectric constant is very low, by the limitations of the limitations of the size of the cut type, but the stability is high, the mechanical quality factor is high, used as a standard frequency control oscillator, high selectivity (more It is a high-frequency bandpass filter and high-frequency, high-temperature ultrasonic transducers.
Because of the specific properties of lead magnesium niobate Pb (Mg1/3Nb2/3)O3 single crystals (Kp ≥ 90%, d33 ≥ 900 × 10-3C/N, ε ≥ 20,000), this material has been studied both at home and abroad, but Because its Curie point is too low, there is still some distance from the use.
Organic Piezoelectric Materials
Also known as piezoelectric polymers, such as polyvinylidene fluoride (PVDF) (thin film) and another organic piezoelectric (film) materials represented by it. This kind of material and its material flexibility, low density, low impedance and high voltage constant (g) and other advantages for the world's attention and the development is very rapid, underwater acoustic ultrasonic measurement, pressure sensing, ignition initiation and other aspects of the application. The disadvantage is that the piezoelectric strain constant (d) is low, making it very limited as an active emission transducer.
The third category is composite piezoelectric materials made up of organic polymer base materials embedded in sheet, rod, rod, or powdered piezoelectric materials. So far, it has been widely used in underwater acoustics, electroacoustics, ultrasound, medicine and other fields. If it is made into a hydroacoustic transducer, it not only has a high hydrostatic pressure response rate but also has impact resistance, is not easily damaged and can be used with different depths