Piezo-/ferroelectric properties

Pyro- and Piezoelectric Properties The electric field application on a ferroelectric nanoceramic/polymer composite creates a macroscopic polarization in the sample, responsible for the piezo- and pyroelectricity of the composite. It is possible to induce ferroelectric behavior in an inert matrix [Huang et al., 2004] or to improve the piezo-and pyroelectricity of polymers. Lam and Chan [2005] studied the influence of lead magnesium niobate-lead titanate (PMN-PT) particles on the ferroelectric properties of a PVDF-TrFE matrix. The piezoelectric and pyroelectric coefficients were measured in the electrical field direction. The Curie point of PVDF-TrFE and PMN-PT is around 105 and 120°C, respectively. Different polarization procedures are possible. As the signs of piezoelectric coefficients of ceramic and copolymer are opposite, the poling conditions modify the piezoelectric properties of the sample. In all cases, the increase in the longitudinal piezoelectric strain coefficient, 33, with ceramic phase poled) at < / = 0.4, the piezoelectric coefficient increases up to 15 pC/N. The decrease in da for parallel polarization is due primarily to the increase in piezoelectric activity of the ceramic phase with the volume fraction of PMN-PT. The maximum piezoelectric coefficient was obtained for antiparallel polarization, and at < / = 0.4 of PMN-PT, it reached 30pC/N. 

Gomes J, Nunes JS, Sencadas V, Lanceros-Mendez S. Influence of the P-phase content and degree of crystallinity on the piezo-and ferroelectric properties of poly (vinyhdene fluoride). Smart Mater Struct 2010 19(6) 065010. 

The ferroelectric property of PVDF form I (and its copolymers) reflects diractly on the hi sl piezo- and pyroelectric effects among the synlh ptri3rmets. Piezoelect strain or stress constant tensor, d or e, are defined, respectively, as follows for the polarization change AP caused by stress a or strain c under the oonditioo of constant temperature and zero electric field ... 

According to Zhong et al. [91], in the homopolymer form of PVDF, the chain confirmation of PVDF is fairly adaptable and crystal polymorphism is often observed with at least four polymorphic phases (a) the non-polar (or paraelectric) TGTG a phase (or form II), (b) polar aU tram p phase (or form I), (c) polar TTTGTITG y phase (or form III), and (d) polar TGTG 5 phase (or form 11 [142,143]. Among these modifications of PVDF, the ferroelectric phases (p, 5, and y) are responsible for the piezo- and ferroelectric properties. That is why numerous research efforts have been devoted to the formation pathways of ferroelecbic PVDF phases. 

The supramolecular structure of block co-polymers allows the design of useful materials properties such as polarity leading to potential applications as second-order nonlinear optical materials, as well as piezo-, pyro-, and ferroelectricity. It is possible to prepare polar superlattices by mixing (blending) a 1 1 ratio of a polystyrene)-6-poly(butadiene)-6-poly-(tert-butyl methacrylate) triblock copolymer (SBT) and a poly (styrene)-Apoly (tert-butyl methacrylate) diblock copolymer (st). The result is a polar, lamellar material with a domain spacing of about 60 nm, Figure 14.10. 

Electrochemical stability at over 4 V is key property high purity solution casting ability to cast thin electrodes from very high (>80%) carbon formulations Orientation under high electrical fields of the beta crystallites in thin films achieves high sensitivity to changes in shape because of pressure (piezo) or temperature (pyro). Considered a ferroelectric material because the remnant polarization is stable. Piezo film for active cancellation of noise in sound absorbing foam laminate... 

The existence or nonexistence of mirror symmetry plays an important role in nature. The lack of mirror symmetry, called chirality, can be found in systems of all length scales, from elementary particles to macroscopic systems. Due to the collective behavior of the molecules in liquid crystals, molecular chirality has a particularly remarkable influence on the macroscopic physical properties of these systems. Probably, even the flrst observations of thermotropic liquid crystals by Planer (1861) and Reinitzer (1888) were due to the conspicuous selective reflection of the helical structure that occurs in chiral liquid crystals. Many physical properties of liquid crystals depend on chirality, e.g., certain linear and nonlinear optical properties, the occurrence of ferro-, ferri-, antiferro- and piezo-electric behavior, the electroclinic effect, and even the appearance of new phases. In addition, the majority of optical applications of liquid crystals is due to chiral structures, namely the ther-mochromic effect of cholesteric liquid crystals, the rotation of the plane of polarization in twisted nematic liquid crystal displays, and the ferroelectric and antiferroelectric switching of smectic liquid crystals. 

PVDF copolymers have been investigated for their piezo properties and for uses in various applications such as sensors. An example of a PVDF copolymer is polyvinylidenefluoride-co-trifluoroethylene [P(VDF-TrFE)], which is a ferroelectric, crystalline polar polymer that exhibits inherent piezoelectric and pyroelectric responses with low acoustic impedance. Such properties provide an optimistic approach towards the use of these polymers for various applications in the near future. Higashihata et al. (1981) compared the piezoelectric craistants of PVDF and P(VDF-TrFE) and observed that much larger values were obtained for P(VDF-TrFE) under the same polarizing conditions. The special interest in this copolymer is also due to the evidence reported by Furukawa et al. (1981) that the PVDF-TrFe copolymer can be annealed to 100% crystallinity, as opposed to 50% in PVDF. Other copolymers have also been explored to determine an enhanced piezo effect (Poulsen and Ducharme, 2010). 

Qiu X, Mellinger A et al (2007) Barrier discharges in cellular polypropylene ferroelectrets how do they influence the electromechanical properties J Appl Phys 101 104112 Qiu X, Hollander L et al (2013) Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets. J Appl Phys 89 4503... 

Ferroelectric liquid crystals are a novel state of matter, a very recent addition to the science of ferroelectrics which, in itself, is of relatively recent date. The phenomenon which was later called ferroelectricity was discovered in the solid state (on Rochelle salt) in 1920 by Joseph Valasek, then a PhD student at the University of Minnesota. His first paper on the subject [1] had the title Piezo-Electric and Allied Phenomena in Rochelle Salt. This was at the time when solid state physics was not a fashionable subject and it took several decades until the importance of the discovery was recognized. Valasek had then left the field. Later, however, the development of this branch of physics contributed considerably to our understanding of the electrical properties of matter, of polar materials in particular and of phase transitions and solid state physics in general. In fact, the science of ferroelectrics is today an intensely active field of research. Even though its technical and commercial importance is substantial, many breakthrough applications may still lie ahead of us. The relative importance of liquid crystals within this broader area is also constantly growing. This is illustrated in Fig. 1,... 

We note that the effect on dielectric, eiccliet, feno-. piezo-, and pyrelectric properties can result from not only the xnre-mentioned materials also dep the grain size of these ceramics [39,42,72-74]. This effect is very important, since electronic devices usittg ferroelectric ceramics, such as multilayer capacitors, have been miniaturized. There have already been many lepoits on grain size dependence in BaTK), ceramic properties [73],... 

---