Ceramic piezoelectrics

An important point now emerges the requirement that the piezoelectric, pyroelectric and ferroelectric effects are restricted to non-centrosymmetric crystals implies that these physical phenomena should not be observed in a polycrystalline solid. This is because the individual grains of a polycrystalline body will polarise in random directions that will cancel overall. This was changed by the discovery, in 1945, of a way to endow polycrystalline ceramic articles with ferroelectric properties. 

The coefficient is called the transverse piezoelectric coefficient. The converse piezoelectric effect, relating strain, e to the applied electric field E is similarly simplified to 

The development of the poling process opened the door to large families of perovskite ceramic materials with properties superior to BaTiOj (BT) for many applications. The major perovskite materials to be utilised over the latter half of the twentieth century were lead-containing ferroelectric ceramic samples derived from lead zirconate PbZrOj (PZ) and lead titanate PbTiOj (PT), including phases in the 

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Table 3. U.S. Ceramic Capacitor and Ceramic Piezoelectric Material Consumption ...

See Lead zirconate titanate ceramics Piezoelectric constants 220 Piezoelectricity 213—221... 

A number of works are devoted to the electrochemical preparation of ZnO, which may have application in photocatalysis, ceramics, piezoelectric transducers, chemical sensors, photovoltaics, and others. ZnO has the same band-gap energy as Ti02, and the oxygenation capacities for both compounds should be similar. Ya-maguchi et al. [155] prepared photoactive zinc oxide films by anodizing a zinc plate. Such films could decompose gaseous acetaldehyde with the aid of black lights. 

In ultrasonic nebulizers, ultrasound waves (Fig. 2) are formed in an ultrasonic nebulizer chamber by a ceramic piezoelectric crystal that vibrates when electrically excited. These set up high-energy waves in the solution, within... 

Silicon piezoresistance Thin-film piezoresistance Ceramic capacitance Thin-film capacitance Ceramic piezoelectricity... 

These materials have shown piezoelectric responses after appropriate poling [18]. Their piezoelectric actuation properties are typically worse than ceramic piezoelectric crystals however, they have the advantages of being lightweight, flexible, easily formed, and not brittle. Additionally, while ceramics are limited to strains on the order of 0.1%, ferroelectric polymers are capable of strains of 10% [91] and very high electromechanical coupling efficiencies [93]. 

FIGURE 31.22 Medical ultrasound image using ceramic piezoelectric transducers. (Scale is in centimeters.)... 

As with ceramic piezoelectric samples, the equation can be simplified. The order of the suffixes takes the same meaning as before, so that it is possible to write... 

Piezoelectric crystals change shape when subjected to an applied potential. The strain in ceramic piezoelectrics is typically small (0.1%), but the operating frequencies can be high (kHz). As mentioned above, quartz is one of the key members of this class of materials. 

A number of works are devoted to the electrochemical preparation of ZnO, which may have application in photocatalysis, ceramics, piezoelectric transducers, chemical sensors, photovoltaics, and others. 

Piezoelectric transducers convert electric energy into ultrasound by applying an osciUating electric field to a piezoelectric crystal (such as quartz). These transducers, which work in liquids or air, can generate frequencies in the megahertz region with considerable power. In addition to natural crystals, ceramic piezoelectric materials, which can be febri-cated into any desired shape, have been developed. 

In the case of based on poly(vinyl alcohol) soluble fibres, SOLVRON-SX, the sonic solicitation was realised using two ceramic piezoelectric transducers, placed at distance of 12.5 and 17.5 cm, respectively, in different conditions of applied force, P. During solicitation step, the experiments were carried out in standard environmental conditions and both in air and acetone (non solvent of PAV). As Table 3.121 shows the solicitation induced in the relaxation stage the corresponding modification of the ultrasonic rate. The dependence of ultrasonation modulus, and rate, v, with the developed force, P, in the solicitation and relaxation stage, respectively, is illustrated in Figures 350 and 351. 

In the brewing industry, there is no ideal foam-control method currently in use, although ultrasonics have been tested to suppress foaming in fermenting vessels. The ultrasound generated by ceramic piezoelectric transducers has the unusual property that when an electric voltage is applied across their crystalline ceramic structure, deformation occurs, so that an alternating current thus produces a sinusoidal vibration. The resonance frequency depends on the physical dimensions of the... 

Ceramics as Dielectrics Barium titanate is used as a miniature capacitor because of its dielectric properties, which include ferroelectric-ity and piezoelectricity. Figure 1.7 shows ceramic piezoelectric parts and assemblies. 

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