Ferroelectrics pyroelectric properties

Both antimony tribromide and antimony ttiiodide are prepared by reaction of the elements. Their chemistry is similar to that of SbCl in that they readily hydroly2e, form complex haUde ions, and form a wide variety of adducts with ethers, aldehydes, mercaptans, etc. They are soluble in carbon disulfide, acetone, and chloroform. There has been considerable interest in the compounds antimony bromide sulfide [14794-85-5] antimony iodide sulfide [13868-38-1] ISSb, and antimony iodide selenide [15513-79-8] with respect to their soHd-state properties, ferroelectricity, pyroelectricity, photoconduction, and dielectric polarization. 

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

Table 11.2 Pyroelectric properties of several thin film ferroelectrics, c = 2.7 X 106 Jm 3K 1...

Compounds belonging to the BaMF4 series display both ferroelectric (M = Co, Ni, Mg, Zn) and pyroelectric properties (M = Fe, Mn) but have estimated Curie temperatures above their melting points125,126. ... 

Table 27.5 lists applications of some of the most commercially important mixed metal, perovskite-t5q)e oxides, and illustrates that it is the dielectric, ferroelectric, piezoelectric (see Section 13.9) and pyroelectric properties of these materials that are exploited in the electronics industry. 

By virtue of their symmetry, ferroelectric smectics are piezoelectric. Polarization can be induced by mechanical shear and, conversely, an electric field can produce shear flow. They also possess pyroelectric properties. 

The third part deals with ferroelectric polymers and their pyroelectric properties. We describe the realization and performance of an IR pyroelectric sensor using copolymers of poly(vinylidene fluoride-ethylene trifluoride). 

Kreher, W. and Rodel, J. 1998. Ferroelectric ceramics and composites statistical models for effective piezoelectric and pyroelectric properties. Applications of Ferroelectrics, 1998, lASF 98, Proceedings of the Eleventh IEEE International Symposium of Ferroelectrics, Edited by E. Colla, D. Damjanovic, and N. Setter, pp 455-458. 

Helgee, B., Hjertberg, T., Skarp, K., Andersson, G., and Gouda, F., Ferroelectric, pyroelectric and electro-optic properties of a chiral side chain copolymer with high polarization and a broad C phase, Liq. Ctyst., 18, 871-878 (1995). 

Choi SW, Shrout TR, Jang SJ, Bhalla AS (1989) Dielectric and pyroelectric properties in the Pb(Mgi/3Nb2/3)03-PbTi03 system. Ferroelectrics 100 29-38 Cross LE (1996) Ferroelectric materials for electromechanical transducer applications. Mater ChemPhys43 108-115... 

Relatively few applications have utilized the ferroelectric effect in ceramics. Ferroelectric ceramics have been widely employed because of the other properties that they display, however. Their dielectric, piezoelectric, and pyroelectric properties have led to their use in capacitor, actuator and other piezoelectric applications, and infrared detection devices. Again, the most widely used materials are the lead-based ABO perovskite compounds. 

It is important to note that all ferroelectric crystals possess piezoelectric and pyroelectric properties. It was also found that all pyroelectric materials are piezoelectric, but the opposite is not true. For example, quartz is piezoelectric but not pyroelectric. At the same time zinc oxide with its wurtzite... 

The chirality in liquid crystal elastomers can be at the origin of additional physical properties such as ferroelectricity, pyroelectricity, circular dichro-ism, and nonlinear optics coupled to the polymer network. Applying external mechanical fields to the elastomers consequently causes electro-... 

Ferroelectric polymer materials like PVDF or its derivatives are mentioned, since they behave as ferroelectric materials (see Fig. 2.2) - They have crystallinity and the crystals show polymorphism by controlling the preparation method. Much detailed work has been carried out on piezoelectric and/or pyroelectric properties, together with their characteristics as electroactive actuators. These materials have long been mentioned as typical electroactive polymers. Through these materials, it is considered that the strain induced in the polymer materials is not large. The electrostrictive coefficient is known to be small for polymers. These are non-ionic polymers and the induced strain originates from the reorientation or the deformation of polarized crystallites in the solid materials. 

Piezoelectric, pyroelectric and ferroelectric materials are often discussed simultaneously, owing to their interrelationship with each other at the crystalline structure level. For a crystalline structure to exhibit piezoelectricity, there should be no symmetry at the inversion centre for point group(s) (Tilley, 2006). A piezoelectric material can show both pyroelectricity (generation of electric charge on a crystal by change of temperature) and ferroelectricity (a property of certain materials that have a spontaneous electric polarisation). The relationship between different types of materials is shown in Figure 9.1. Ferroelectric materials are known to have superior piezoelectric properties over their non-feiroelectric counterparts. 

A ferroelectric is formally defined as a pyroelectric material that has a reversible, or switchable , polarisation. Ferroelectricity was discovered in ca 1920 by Valasekt in Rochelle salt (NaKC4H406 4H2O) - a material that was known at the time for its piezoelectric and pyroelectric properties. For years after this discovery, ferroelectricity was... 

Ferroelectric materials with piezoelectric and pyroelectric properties that may find applications in diverse gauges, field-effect transistors, random access memory devices [250]. 

Some liquid-crystalline materials contain smectic phases which give ferroelectric and pyroelectric properties and are proposed for use in optical shutters, displays and heat sensors, as has been discussed by Simmonds in Chapter 7. 

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