Piezoelectric Coefficients and: Combination of Properties at Specific Microgeometry

Piezoelectric coefficients eij are used to describe a link between an external mechanical strain and a piezoelectric polarisation caused by the direct piezoelectric effect. The piezoelectric coefficients eij are of importance to analyse a link between a mechanical stress and an external electric field at the converse piezoelectric effect. Examples of the piezoelectric sensitivity of composites with various connectivity patterns are discussed in terms of the effective piezoelectric coefficients and relations between the piezoelectric coefficients and Of specific interest are a non-monotonic behaviour of large values of and considerable anisotropy of as well as their links to the microgeometry and properties of components

New effects in 1–3-type composites based on relaxor-ferroelectrics single crystals

Two effects of the matrix subsystem on the piezoelectric performance and hydrostatic parameters are first studied in novel 1–0–3 composites that contain relaxor-ferroelectric single-crystal rods surrounded by a ferroelectric ceramic/ polymer matrix with 0–3 connectivity. First, the influence of the mutual orientation of the poling direction of the single-crystal and ceramic components on the properties of the 1–0–3 composite is discussed to demonstrate advantages concerned with the high hydrostatic piezoelectric performance and large anisotropy of squared figures of merit. In a 1–0–3 0.67Pb(Mg1/3Nb2/3)O3 − 0.33PbTiO3 single crystal/ (Pb1–xCax)TiO3 ceramic/araldite composite with x = 0.20–0.25, values of max g_ h * 102 mV · m/N and max(d_ hg_ h) * 10−11 Pa−1 are achieved at specific volume-fraction and rotation-angle ranges due to the new orientation effect in the presence of a highly anisotropic 0–3 matrix. Second, the influence of the aspect ratio of ceramic inclusions on the piezoelectric and hydrostatic parameters of the 1– 0–3 composite based on relaxor-ferroelectric SCs is studied. In this case, the elastic anisotropy of the 0–3 matrix plays the key role in forming the large effective parameters of the composite. The studied composites can be used in piezoelectric sensor, energy-harvesting and hydrophone applications

Improving Piezoelectric Sensitivity

The piezoelectric sensitivity of the composite is described in terms of four types of the piezoelectric coefficients, and The role of each type of the piezoelectric coefficients and its merit in determining the PS in composites with various microgeometric features are discussed. Diagrams that link electric and mechanical fields and contain the four types of the piezoelectric coefficients are represented for the direct and converse piezoelectric effects. Examples of orders-of-magnitude of the aforementioned piezoelectric coefficients are given for modern composites based on single crystals. Some ways for improving the piezoelectric sensitivity of the composites are discussed

Novel lead-free composites with two porosity levels: Large piezoelectric anisotropy and high sensitivity

A novel lead-free 1-3-type composite based on a ferroelectric domain-engineered single crystal is put forward. In the porous polymer matrix of this composite, two different porous structures are observed, and the effect of these structures on the piezoelectric performance, electromechanical coupling and related anisotropy parameters of 1-3-type composites is first studied. New diagrams that link the volume fractions of the single-crystal component and the porous regions in the polymer medium are built to show validity of conditions for a large anisotropy of piezoelectric coefficients d3j∗ and electromechanical coupling factors k3j∗, kt∗ and kp∗. In the composites based on the complex alkali niobate alkali tantalate single crystal with small piezoelectric anisotropy (d331)/|d311)| = 2.1), the three anisotropy factors d33∗/|d31∗| ≥ 5, k33∗/|k31∗| ≥ 5 and kt∗/|kp∗| ≥ 5 hold simultaneously due to the presence of layers with heavily prolate and heavily oblate air pores in the porous polymer matrix. The two porosity levels influence the elastic anisotropy of the porous matrix, and this leads to an increase in the three anisotropy factors across wide volume-fraction ranges. Of independent interest is the high piezoelectric sensitivity of the composites for which the condition g33∗ ≥1 V m N-1 holds at their piezoelectric coefficient d33∗ ≈ (200-500) pC N-1 and electromechanical coupling factors k33∗ ≈ kt∗ ≈ 0.8-0.9. The studied parameters of the novel piezo-active 1-3-type composites are of value for various applications such as active elements of piezoelectric transducers, energy-harvesting devices and sensors

Effective Piezoelectric Coefficients: From Microgeometry to Anisotropy

Piezoelectric coefficients dij are most widespread to describe the piezoelectric effect, electromechanical properties and other related parameters. The effective piezoelectric coefficients and their links to sensitivity are discussed for piezo-active composites with various connectivity patterns. Examples of the piezoelectric sensitivity of the 2–2-type, 1–3-type, 1–1-type, 0–3-type, and 3–β composites based on ferroelectics are considered. The role of the microgeometry in forming the piezoelectric sensitivity and anisotropy of the piezoelectric coefficients is analysed. Ways to improve the piezoelectric sensitivity in terms of are discussed in connection with potential piezotechnical applications

Microgeometry of Composites and Their Piezoelectric Coefficients g*ij

Piezoelectric coefficients gij represent a link between an external mechanical stress applied to a sample and an electric field formed by polarisation charges of the sample as a result of the direct piezoelectric effect. The piezoelectric coefficients gij also characterise a link between a strain and electric displacement at the converse piezoelectric effect. The piezoelectric sensitivity associated with gij is of importance for sensor, energy-harvesting, acoustic, and hydroacoustic applications, for piezo-ignition systems, etc. Examples of the effective piezoelectric coefficients max and their links to the piezoelectric coefficients are discussed for piezo-active composites with various connectivity patterns (2–2-type, 1–3-type, 1–1-type, 0–3-type, and 3–β composites). The important role of the microgeometric factor and polymer component at achieving the large values of of the composite is shown