Commonly used piezoelectric material classification

The first category is inorganic piezoelectric materials, which are divided into piezoelectric crystals and piezoelectric ceramics. Piezoelectric crystals generally refer to piezoelectric single crystals; piezoelectric ceramics generally refer to piezoelectric polycrystals. Piezoelectric ceramics refer to polycrystals formed by mixing, forming and sintering at high temperature with the necessary raw materials, and the fine grains obtained by the solid-phase reaction between the powder particles and the sintering process are randomly aggregated. Ceramics with piezoelectricity are called piezoelectric ceramics, which are actually ferroelectric ceramics. There are ferroelectric domains in the grains of this ceramic. The ferroelectric domains are composed of 180 domains whose spontaneous polarization directions are antiparallel and 90 domains whose spontaneous polarization directions are perpendicular to each other. Under the condition of DC electric field), the spontaneous polarization is fully arranged according to the direction of the external electric field and maintains the remnant polarization after the removal of the external electric field, so it has macroscopic piezoelectricity. Such as: barium titanate BT, lead zirconate titanate PZT, modified lead zirconate titanate, lead metaniobate, lead barium lithium niobate PBLN, modified lead titanate PT, etc. The successful development of such materials has promoted the improvement and enhancement of the performance of various piezoelectric devices of acoustic transducers and piezoelectric sensors.       Piezoelectric crystal generally refers to a piezoelectric single crystal, which refers to a crystal grown in a long-range order according to the crystal space lattice. This crystal structure has no center of symmetry and is therefore piezoelectric. Such as crystal (quartz crystal), lithium gallate, lithium germanate, titanium germanate and iron transistor lithium niobate, lithium tantalate, etc.       In comparison, piezoelectric ceramics have strong piezoelectricity, high dielectric constant, and can be processed into any shape, but have low mechanical quality factor, large electrical loss, and poor stability, so they are suitable for high-power transducers and broadband filtering. However, it is not ideal for high frequency and high stability applications. Piezoelectric single crystals such as quartz have weak piezoelectricity, low dielectric constant, and size limitations due to the cut shape, but they have high stability and high mechanical quality factor. They are mostly used as oscillators for standard frequency control, high selectivity (more It belongs to high-frequency narrow band-pass) filters and high-frequency and high-temperature ultrasonic transducers. Recently, due to the specific properties of lead magnesium niobate Pb(Mg1/3Nb2/3)O3 single crystal (Kp ≥90%, d33≥900×10-3C/N, ε≥20,000), research on this material has begun at home and abroad. But because its Curie point is too low, there is still a long way to go.The second category is organic piezoelectric materials, also known as piezoelectric polymers, such as polyvinylidene fluoride (PVDF) (film) and other organic piezoelectric (film) materials represented by others. Such materials and their materials are flexible, low density, low impedance and high voltage voltage constant (g) and other advantages have attracted worldwide attention, and the development is very rapid. . The disadvantage is that the piezoelectric strain constant (d) is low, so that it is greatly limited as an active emission transducer. The third category is composite piezoelectric materials, which are composed of sheet-like, rod-like, rod-like, or powder-like piezoelectric materials embedded in organic polymer base 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 is impact resistant, not easily damaged and usable with different depths.