Piezoelectric materials

Scaiming probe microscopies have become the most conspicuous surface analysis tecimiques since their invention in the mid-1980s and the awarding of the 1986 Nobel Prize in Physics [71, 72]- The basic idea behind these tecimiques is to move an extremely fine tip close to a surface and to monitor a signal as a fiinction of the tip s position above the surface. The tip is moved with the use of piezoelectric materials, which can control the position of a tip to a sub-Angstrom accuracy, while a signal is measured that is indicative of the surface topography. These tecimiques are described in detail in section BI.20. 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

Approximately 40% of the U.S. electronic ceramics industry is represented by ferroelectrics. Table 3 shows U.S. consumption of ceramic capacitors and piezoelectric materials (109). 

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

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

Typical piezoelectric materials are ceramic crystals and copolymers, such as poly(vinyHdene fluoride-i o-trifluoroethylene),... 

CH2—CI2—) —(—CF2— CFH—) (39). Ceramic crystals have a higher piezoelectric efficiency. Their high acoustic impedance compared to body tissues necessitates impedance matching layers between the piezoelectric and the tissue. These layers are similar in function to the antireflective coatings on a lens. Polymer piezoelectric materials possess a more favorable impedance relative to body tissues but have poorer performance characteristics. Newer transducer materials are piezoelectric composites containing ceramic crystals embedded in a polymer matrix (see Composite materials, polymer-MATRIX Piezoelectrics). 

Pyroelectrics. Pyroelectric ceramics are materials that possess a uoique polar axis and are spontaneously polarized ia the abseace of an electric field. Pyroelectrics are also a subset of piezoelectric materials. Ten of the 20 crystal classes of materials that display the piezoelectric effect also possess a unique polar axis, and thus exhibit pyroelectricity. In addition to the iaduced charge resultiag from the direct pyroelectric effect, a change ia temperature also iaduces a surface charge (polarizatioa) from the piezoelectric aature of the material, and the strain resultiag from thermal expansioa. 

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

The main categories of electrical/optical ceramics are as follows phosphors for TV, radar and oscilloscope screens voltage-dependent and thermally sensitive resistors dielectrics, including ferroelectrics piezoelectric materials, again including ferroelectrics pyroelectric ceramics electro-optic ceramics and magnetic ceramics. 

Changes in polarization may be caused by either the input stress profile or a relaxation of stress in the piezoelectric material. The mechanical relaxation is obviously inelastic but the present model should serve as an approximation to the inelastic behavior. Internal conduction is not treated in the theory nevertheless, if electrical relaxations in current due to conduction are not large, an approximate solution is obtained. The analysis is particularly useful for determining the signs and magnitudes of the electric fields so that threshold conditions for conduction can be established. 

The science and technology of piezoelectric materials has long been dominated by the availability of specific materials with particular properties. Piezoelectric polymers are the most recent class of piezoelectrics developed. 

Since discovering and making use of the piezoelectric effect in naturally occurring crystals such as quartz and Rochelle salts, scientists have produced a wide range of piezoelectric materials in the laboratoi y. An early example is barium titanate, used in an electrical component called a capacitor. Currently, most piezoelectric materials are oxide materials based on lead oxide, zirconate oxide, and titanium. These very hard piezoelectric materials are termed piezoceramics. 

Temperature can destroy the piezoelectric properties of the probe, although techniques for cooling probes (delay blocks), and development of temperature-resistant piezoelectric materials, are extending the temperature range. Differences of up to 5% in thickness can occur between hot and cold readings. 

Actual problems of production and application of ferro- and piezoelectric materials) NIITEKhIM, Moscow, (1984) 469. 

A.I. Agulyansky, V.T. Kalinnikov, Actual problems of preparation and application of ferroelectric and piezoelectric materials. Abstracts of III Vses. Confer. Moscow NIITEChlM 1987 p. 15 (in Russian). 

The initial stages of the STM experiment require the positioning of the tip in proximity of the surface such that a tunnelling current can be detected this often means moving the tip by several micrometres or even millimetres. The piezoelectric materials used for scanning are not suitable for this initial approach and most instruments therefore contain a second coarse positioning driver frequently this is also a piezoelectric material in a stick-slip kind of design.27... 

In his work, Wallace [12] formed inkjet printheads from the rectangular blocks made of piezoelectric material. A diamond saw is used to create fluid channel grooves and channel actuator structures. These grooves are approximately 1 pm apart, 360 pm deep and 170 pm wide. Next, a cover plate is attached to the top of the grooves to form an enclosed rectangle channel for the working fluids. A polymer orifice plate (see Fig. 11.3) with many 40 pm diameter orifices is attached to the other end of the grooves. 

A variety of piezoelectric transducers have been employed for PAC. Ceramic transducers, usually lead zirconate titanate, are most commonly employed because of their sensitivity, time resolution and commercial availability. However, their acoustic response is often dominated by their own resonance, and so polymeric film detectors, such as polyvinylidenedifluoride, are often used. These piezoelectric materials are non-resonant, but not as sensitive as the ceramic detectors. Again, each detector has its own advantages (and disadvantages).14,15... 

Electricity production, using hydrothermal steam, 12 529-530 Electricity supply, operation and maintenance of, 10 159 Electric melting, 23 253 Electric motors, 10 149 Electric polarization, in piezoelectric materials, 22 709-710 Electric potential, 9 739 Electric potential difference, exponents of dimensions, 8 585t Electric power. See also Electricity production... 

Mechanical scales, 26 229-236 functionality of, 26 251 Mechanical seals, for pumps, 21 81 Mechanical strength measurement, in tire compounding, 21 811 Mechanical stress, in piezoelectric materials, 22 709... 

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