Electromechanical anisotropy

An important aspect of the enhanced intrinsic response of ferroelectrics is anisotropy, the direction dependence of properties. By symmetry, ferroelectric crystals are anisotropic with respect to dielectric, mechanical, and electromechanical properties, and this issue is essential when designing devices that exploit the highest material responses by correctly orienting single crystals [8, 33-35]. The crystal axes, along which the highest material response occurs, may not coincide with the polar directions of spontaneous polarization for a given ferroelectric phase. This is the case... 

These normalized electromechanical equations are applicable to any chemistry, and allow you tailor the optimal single-crystal intrinsic response. Furthermore, any improvement on the chemistry of a ferroelectric material will asymptotically converge to an optimal orientation of 54.76° for materials with weak anisotropy, or to zero in the limit of A.. = 2/3. 

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). 

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... 

Figure 11). It can be accoimted for by the presence of FC with the large piezoelectric anisotropy and by comparable values of electromechanical constants of the SC and FC components in the composite. Values of the piezoelectric coefficients d and 33 (see... 

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