Piezoelectric effect, ferroelectrics

Polymer Ferroelectrics. In 1969, it was found that strong piezoelectric effects could be induced in the polymer poly(vinyhdene fluoride) (known as PVD2 or PVDF) by apphcation of an electric field (103). Pyroelectricity, with pyroelectric figures of merit comparable to crystalline pyroelectric detectors (104,105) of PVF2 films polarized this way, was discovered two year later (106.)... 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

Fig. 5.19. Shock-induced volume polarizations have been observed in a wide range of solids due to a number of different physical phenomena, including piezoelectricity and ferroelectricity. The signals observed from polymers and ionic crystals are not due to established phenomena, and are described as due to shock-induced polarization effects.

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

Ferroelectrics. Among the 32 crystal classes, 11 possess a centre of symmetry and are centrosymmetric and therefore do not possess polar properties. Of the 21 noncentrosymmetric classes, 20 of them exhibit electric polarity when subjected to a stress and are called piezoelectric one of the noncentrosymmetric classes (cubic 432) has other symmetry elements which combine to exclude piezoelectric character. Piezoelectric crystals obey a linear relationship P,- = gijFj between polarization P and force F, where is the piezoelectric coefficient. An inverse piezoelectric effect leads to mechanical deformation or strain under the influence of an electric field. Ten of the 20 piezoelectric classes possess a unique polar axis. In nonconducting crystals, a change in polarization can be observed by a change in temperature, and they are referred to as pyroelectric crystals. If the polarity of a pyroelectric crystal can be reversed by the application on an electric field, we call such a crystal a ferroelectric. A knowledge of the crystal class is therefore sufficient to establish the piezoelectric or the pyroelectric nature of a solid, but reversible polarization is a necessary condition for ferroelectricity. While all ferroelectric materials are also piezoelectric, the converse is not true for example, quartz is piezoelectric, but not ferroelectric. 

The piezoelectric effect is an electromechanical effect in which mechanical evoke and reverse an electric reaction in a ferroelectric material and vice versa. The word piezo has been derived from the Greek piezein which means press . Compounds are composed of positive and negative ions and are electrically neutral as a whole. The fact that electrically charged particles are still present in the crystal can for example be demonstrated by means of the electric... 

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... 

In many ferroelectric materials, the net piezoelectric effect is a result of both intrinsic and extrinsic responses. Here, intrinsic refers to the response that would result from an appropriately oriented single crystal (or ensemble thereof, in a polycrystalline sample). The extrinsic response is typically the result of motion of non-180° domain walls. The principle of these... 

In Eq. (20) the three terms are related to the Maxwell stress (first), piezoelectric effect (second) and electrostriction (third). In order to obtain information about ferroelectricity via piezoresponse measurements, we need a link between the spontaneous polarisation and the piezoelectric constant. According to Furukawa and Damjanovic, piezoelectricity in ferroelectrics can be explained as electrostriction biased by the spontaneous polarisation if their paraelectric phase is nonpolar and centrosymmetric [461, 495, 496]. Therefore the d33 constant depends on the spontaneous polarisation P5 ... 

The improper ferroelectricity origin can be roughly explained in the following way, see Fig. 4.31a. Elastic strain induces the polarization vector F, dil]uki via the flexoelectric and piezoelectric effects. Since the strain... 

Eliseev, E.A. Complete symmetry analysis of the surface-induced piezomagnetic, piezoelectric and linear magnetoelectric effects. Ferroelectrics 417, 100-109 (2011)... 

Piezoelectricity and ferroelectricity are the result of electric dipole effects that are due to ions shifting from their initial positions in the lattice. This effect, which is strongly structure-dependent, was discussed above. Pyroelectric materials have permanent electric dipole moments, their magnitude varying with temperature. In infrared detectors, use is made of the ferroelectric phase transitions in perovskites. 

Davis et al. [42] have recently introduced the terms rotator and extender for a variety of ferroelectrics based on oxygen octahedra, in order to classify them with respect to whether the shear or the collinear effect dominates in the piezoelectric response. In extenders, the dominant polarization extension is directly related to the collinear piezoelectric effect, whereas in rotators the dominant contribution to the piezoelectric effect is the polarization rotation, that is directly related to the shear piezoelectric effect. Thus, extenders are ferroelectrics with a large longitudinal piezoelectric coefficient 33 that is related to a large relative dielectric susceptibihty %33, while rotators are ferroelectrics with large shear coefficients dis and 24. which are related to transverse susceptibilities and %2z. correspondingly. Electrostrictive... 

Damjanovic, D. 2005. Contributions to the piezoelectric effect in ferroelectric single crystals and ceramics. Journal of the American Ceramic Society 88 [10] 2663-2676. 

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