Electrostriction

Electrostriction, which is a change in sample dimensions in response to the application of an electric field to a dielectric, is a universal characteristic and provides another example of an electromechanical effect. Some materials get thinner while others get thicker in the direction of the electric field. This effect is not reversible and a deformation does not produce any polarisation. The effect is found in all materials, not just those that lack a centre of symmetry, including glasses and hquids. However, the electrostrictive effect is generally very small except for ferroelectric perovskites, especially relaxor ferroelectrics described in the following (Section 6.7). 

Electrostriction is related to the converse piezoelectric effect. At modest electric field strengths, the piezoelectric equations given previously are adequate and there is a linear relationship between strain and electric field. However, at higher electric field strengths, these equations need to be extended to include a further term quadratic with respect to the electric field. The strain is now given by 

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 

In the vicinity of each ion, a certain shrinkage of the solvent is likely to occm as a result of the attraction between the ionic charge and the polar molecules. This is called electrostriction, and leads to a local increase in the density of the solvent around each ion since more molecules will be packed around the ion than would be present in that volume were the ion not present. 

Electrostriction is important in solvation, but has not ever been properly incorporated in any detail into electrolyte theory. 

Dielectric materials always display an elastic deformation when stressed by an electric field due to displacements of ions within the crystal lattice. The mechanism of polarization, i.e., the shifting of ions in the direction of an applied field, results in a constriction of surrounding ions in the atomic lattice, as restoring forces between atoms seek to balance the system. This behavior is called electrostriction and is common to all crystals endowed with a center 

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Electrostrictive materials are materials that exhibit a quadratic relationship between mechanical stress and the square of the electric polari2ation (14,15). Electrostriction can occur in any material. Whenever an electric field is appHed, the induced charges attract each other, thus, causing a compressive force. This attraction is independent of the sign of the electric field and can be approximated by... 

The strain j Hes along the axis of the electric field, E, or most often along the axis of the induced polari2ation, P. The electrostrictive coefficients for the electric field and polari2ation are M and respectively. Electrostriction is a small effect. In contrast to pie2oeIectric materials, electrostrictive materials... 

Typical electrostrictive materials include such compounds as lead manganese niobate lead titanate (PMN PT) and lead lanthanium 2irconate titanate (PLZT). Electrostriction is a fourth-rank tensor property observed in both centric and acentric insulators (14,15). 

This class of smart materials is the mechanical equivalent of electrostrictive and magnetostrictive materials. Elastorestrictive materials exhibit high hysteresis between strain and stress (14,15). This hysteresis can be caused by motion of ferroelastic domain walls. This behavior is more compHcated and complex near a martensitic phase transformation. At this transformation, both crystal stmctural changes iaduced by mechanical stress and by domain wall motion occur. Martensitic shape memory alloys have broad, diffuse phase transformations and coexisting high and low temperature phases. The domain wall movements disappear with fully transformation to the high temperature austentic (paraelastic) phase. 

Piezoelectric and Electrostrictive Device Applications. Devices made from ferroelectric materials utilizing their piezoelectric or electrostrictive properties range from gas igniters to ultrasonic cleaners (or welders) (72). 

Multilayer-type piezoelectric or electrostrictive actuators are used for several apphcations including the composite smart stmcture shown in Figure 9... 

S. J. Jang, Electrostrictive Ceramics for Transducer Applications, Ph.D. dissertation. The Pennsylvania State University, University Park, 1979. 

The dielectric constants of amino acid solutions are very high. Thek ionic dipolar structures confer special vibrational spectra (Raman, k), as well as characteristic properties (specific volumes, specific heats, electrostriction) (34). 

Piezoelectrics. AH ceramics display a slight change ia dimension, or strain, under the appHcation of an electric field. When the iaduced strain is proportional to the square of the field iatensity, it is known as the electrostrictive effect, and is expressed by ... 

Due to their high piezoelectric response, electrostriction in ferroelectrics, induced by an applied electric field, can be used as strain-inducing components (just as ferromagnetic materials can be exploited for their magnetostriction). Thus barium... 

Table 4J. Electrostrictive constants (after Davison and Graham [79D01]).

From the experimental results and theoretical approaches we learn that even the simplest interface investigated in electrochemistry is still a very complicated system. To describe the structure of this interface we have to tackle several difficulties. It is a many-component system. Between the components there are different kinds of interactions. Some of them have a long range while others are short ranged but very strong. In addition, if the solution side can be treated by using classical statistical mechanics the description of the metal side requires the use of quantum methods. The main feature of the experimental quantities, e.g., differential capacitance, is their nonlinear dependence on the polarization of the electrode. There are such sophisticated phenomena as ionic solvation and electrostriction invoked in the attempts of interpretation of this nonlinear behavior [2]. 

We set out with the idea that, in the vicinity of each ion in solution there is likely to be a certain amount of electrostriction—a certain shrinkage of the solvent caused by the attraction between the ionic charge and the polar molecules. In order to estimate from experimental data how much shrinkage, if any, has taken place, we must start with a correct idea of what would have been the volume of the solution, if no shrinkage had taken place. In making a comparative study of various solutes, we need a common basis for comparison. Since this is not provided by the volumes of the crystalline solids, we may try a different approach. We may compare the addition of any pair of ions to the solvent with the addition of a pair of solvent molecules. 

Let us now ask how this value could be used as a basis from which to measure the local disturbance of the water structure that will be caused by each ionic field. The electrostriction round each ion may lead to a local increase in the density of the solvent. As an example, let us first consider the following imaginary case let us suppose that in the neighborhood of each ion the density is such that 101 water molecules occupy the volume initially occupied by 100 molecules and that more distant molecules are not appreciably affected. In this case the local increase in density would exactly compensate for the 36.0 cm1 increment in volume per mole of KF. The volume of the solution would be the same as that of the initial pure solvent, and the partial molal volume of KF at infinite dilution would be zero. Moreover, if we had supposed that in the vicinity of each ion 101 molecules occupy rather less than the volume initially occupied by 100 molecules, the partial molal volume of the solute would in this case have a negative value. 

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],... 

The information content of AV and AS is similar. Values of AV are usually more precise than those of AS, although they require specialized apparatus for their measurement. If ions are being formed in the activation step, AV may be -20 cm3 mol-1. This effect reflects the electrostriction of the solvent. If the transition state features bond breaking, as in an SnI reaction, AV 10 cm3 mol-1. Conversely, AV -10 cm3 mol-1 is characteristic of bond making. 

Electrostrictive Stress 0.2—2 MPa Small strains, but large forces, easy Elimination of hysteresis effects... 

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