Piezoelectricity, electromechanical properties

Far more frequently, however, measurements are made with a relatively thin film (often < 5 /rm) on a comparatively massive substrate (often > 400 //,m in thickness). In principle, the piezoelectric and electromechanical properties of the films can be extracted by fitting conventional resonance measurements. In practice, multiple resonances due to the film/substrate system are measured it is then necessary to deconvolute the data in order to extract information on the films itself. In practice, this is difficult to do unambiguously [21,22],... 

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]. 

The purpose of this section is to explain the mechanism and key components required for developing piezoelectricity in amorphous polymers and to present a summary of the polarization and electromechanical properties of the amorphous polymers currently imder investigation. 

Linear electromechanical properties - elastic, piezoelectric and dielectric -including their temperature coefficients for a-quartz are summarized in Table 7.2. Temperature dependence of the piezoelectric coefficients d, du is moreover displayed in Fig. 7.4. This temperature behavior is very important for the applications of quartz in sensors. 

Ilyaev AB, Umarov BS, Shabanova LA, Dubovik MF (1986) Temperature dependence of electromechanical properties of LGS crystals. Phys Stat Sol (a) 98 K109-K114 IRE Standards on Piezoelectric crystals. Proc IRE (1949) 37 1378 Jaffe B, Cook WR, Jaffe H (1971) Piezoelectric ceramics. Academic, London Jayasundere N, Smith BV (1993) Dielectric constant for binary piezoelectric 0-3 composites. J Appl Phys 73 2462-2466... 

Kaminskii AA, Belokoneva EL, Mill BV, Pisarevskii YuV, Sarkisov SE, Silvestrova IM, Butashin AV, Khodzhabagyan GG (1984) Pure and Nd -Doped Ca3Ga2Ge40i4 and Sr3Ga2Ge40i4 single erystals, their strueture, optical, spectral, luminiscence, electromechanical properties and stimulated emission. Phys Stat Sol (a) 86 345-362 Kar Lai Ng, Chan HLW, Choy ChL (2000) Piezoelectric and Pyroelectric Properties of PZT/P(VDF-TrFE) Composites with constituent phases poled in parallel or antiparallel directions. IEEE Trans UFFC 47 1308-1315... 

Rosen CZ, Hiremath BV, Newnham R (eds) (1992) Piezoelectricity. Springer-Verlag, New York Roy S, Basu S (2002) Improved zinc oxide film for gas sensor apphcations. BuU Mater Sci 25 513-515 Sanchez-Pedreno JAO, Drew PKP, Alder JF (1986) The investigation of coating materials for the detection of nitrobenzene with coated quartz piezoelectric crystals. Anal Chim Acta 182 285-291 Scheide EP, Taylor JK (1974) Piezoelectric sensor for mercury in air. Environ Sci Technol 8 1087-1091 Schulz M, Sauerwald J, Richter D, Fritze H (2009) Electromechanical properties and defect chemistry of Mgh-temper-ature piezoelectric materials. Ionics 15 157-161... 

An overview of the piezoeJectric activity in amorphous piezoelectric polymers is presented. The criteria required to render a polymer piezoelectric are discussed. Although piezoelectricity is a coupling between mechanical and electrical properties, most research has concentrated on the electrical properties of potentially piezoelectric polymers. In this work, we present con arative mechanical data as a function of temperature and offer a summary of polarization and electromechanical properties for each of the polymers considered. 

In die late nineteenth century, scientists quickly adopted flie seminal publications of the Curie brothers. Consequently, piezoelectricity and electrostriction were first discovered and investigated on inorganic, mono- or polycrystalline materials (Katzir 2006). Therefore, the theoretical treatment of tire relevant electromechanical properties has been based on the physics and in particular on the structure and the anisotropy of crystals (Newnham 2005 Tichy et al. 2010). Semicrystalline or amorphous polymers are usually less anisotropic flian crystals, and the symmetry... 

In this eontext, ferroelectrets actually represent a third elass of piezoelectric polymers in the sense that these cellular materials share features of charge electrets (real eharges) with those of ferroelectric polymers (hysteresis-type ED characteristics) (Bauer et al. 2004 Lekkala et al. 1996). Moreover, ferroelectrets are characterized by extremely high piezoelectric 33 coefficients as well as an extreme anisotropy in their mechanical and electromechanical properties, which partially require speeifie characterization techniques (Dansachmiiller et al. 2005). 

P(VDCN-VAc) has been used in ultrasonic transducers as a thickness extensional (TE) mode resonator. The transducer of piezoelectric fluoropolymers. PVDF and/or P(VDF-TVFE), is well known in medical applications. Ihble 3 lists data on the electromechanical properties of P(VDCN-VAc), P> F. and PZT. Ekctmmechanical coupling frurtor K, of these polymers is 0 J-0 J, which is larger than that of quartz but substantially... 

H. Ohigashi. Electromechanical properties of polarized polyvinylideoe fluoride films as studied by the piezoelectric resonance method, J. AppL Pkys. 47 949 (1976)... 

Theoretical study of the propagation of the elastic wave in 1-3 composites [8334.147-149] enable one to indicate how electromechanical properties oi piezoelectric composites depend on the properties of the component phases and the volume fraction of tte piezoelectric ceramics. The dependence between electromechanical coupling foctor k) and the acoustic impedance (Z) can be determined theoretically for composites of d erent ceramic contents and to find a compromise between increasing k and Z while increasing ceramic contents. High values of coefficient k and small acoustic impedance Z are required in applications for ultrasonic transducers. 

Some materials (especially crystalline) tend to show electromechanical properties which means that the material is stretched when voltage is applied. Closely packed piezoelectric crystals are very effective electroacoustic COTiverters and can be used as acoustic sources. 

To predict the effective electromechanical properties of the 0-3 composite with the spheroidal inclusions, different averaging methods are applied [15, 16, 23-25]. Our current study is carried out within the framework of the model [15] that has first been applied to the 0-3 composite based on the (Pbi.jrCai)Ti03 FC with the large piezoelectric anisotropy. In this model the shape of each inclusion (Figure 1, component 1) is described by the equation... 

The calculation procedure is based on the effective field method (EFM), i.e., the Mori -Tanaka method [26] generalized for heterogeneous piezoelectric media [16, 23], The EFM based on Eshelby s concept of spheroidal inclusions [27, 28] is a variant of the self-consistent scheme for the calculation of effective constants of the piezoactive composites. Following the EFM, we take into account the electromechanical interaction between the piezo-active inclusions in the matrix and related coupled effects. The effective electromechanical properties of the 0-3 composite are represented in the matrix form as... 

Ferroelectric Ceramic—Polymer Composites. The motivation for the development of composite ferroelectric materials arose from the need for a combination of desirable properties that often caimot be obtained in single-phase materials. For example, in an electromechanical transducer, the piezoelectric sensitivity might be maximized and the density minimized to obtain a good acoustic matching with water, and the transducer made mechanically flexible to conform to a curved surface (see COMPOSITE MATERIALS, CERAMiC-MATRix). 

The semiconducting properties of the compounds of the SbSI type (see Table XXVIII) were predicted by Mooser and Pearson in 1958 228). They were first confirmed for SbSI, for which photoconductivity was found in 1960 243). The breakthrough was the observation of fer-roelectricity in this material 117) and other SbSI type compounds 244 see Table XXIX), in addition to phase transitions 184), nonlinear optical behavior 156), piezoelectric behavior 44), and electromechanical 183) and other properties. These photoconductors exhibit abnormally large temperature-coefficients for their band gaps they are strongly piezoelectric. Some are ferroelectric (see Table XXIX). They have anomalous electrooptic and optomechanical properties, namely, elongation or contraction under illumination. As already mentioned, these fields cannot be treated in any detail in this review for those interested in ferroelectricity, review articles 224, 352) are mentioned. The heat capacity of SbSI has been measured from - 180 to -l- 40°C and, from these data, the excess entropy of the ferro-paraelectric transition... 

Because of its piezoelectric properties, synthetic CC-quartz is used for frequency control in electrical oscillators and filters and in electromechanical transducers. When mechanically stressed in the correct direction, CC-quartz develops an electric polarization. The opposite is also tme an applied electric field gives rise to a mechanical distortion in the crystal. Thin sections of quartz are cut to dimensions that produce the desired resonance frequency when subjected to an alternating electric field the vibrating crystal then reacts with the driving circuit to produce an oscillation that can be narrowly controlled. Quartz is ideal for this application because it is hard, durable, readily synthesized, and can be tuned to high accuracy, for example, quartz crystal clocks can be made that are stable to one part in 109. 

The class of ferroelectric materials have a lot of useful properties. High dielectric coefficients over a wide temperature and frequency range are used as dielectrics in integrated or in smd (surface mounted device) capacitors. The large piezoelectric effect is applied in a variety of electromechanical sensors, actuators and transducers. Infrared sensors need a high pyroelectric coefficient which is available with this class of materials. Tunable thermistor properties in semiconducting ferroelectrics are used in ptcr (positive temperature coefficient... 

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