Pyroelectrics nonlinear

The most important materials among nonlinear dielectrics are ferroelectrics which can exhibit a spontaneous polarization PI in the absence of an external electric field and which can spHt into spontaneously polarized regions known as domains (5). It is evident that in the ferroelectric the domain states differ in orientation of spontaneous electric polarization, which are in equiUbrium thermodynamically, and that the ferroelectric character is estabUshed when one domain state can be transformed to another by a suitably directed external electric field (6). It is the reorientabiUty of the domain state polarizations that distinguishes ferroelectrics as a subgroup of materials from the 10-polar-point symmetry group of pyroelectric crystals (7—9). 

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],... 

Theoretical estimations and experimental investigations tirmly established (J ) that large electron delocalization is a perequisite for large values of the nonlinear optical coefficients and this can be met with the ir-electrons in conjugated molecules and polymers where also charge asymmetry can be adequately introduced in order to obtain non-centrosymmetric structures. Since the electronic density distribution of these systems seems to be easily modified by their interaction with the molecular vibrations we anticipate that these materials may possess large piezoelectric, pyroelectric and photoacoustic coefficients. 

The above conclusions introduce intrinsic limitations to the use of the ID conjugated systems in nonlinear optical devices. Although these may benefit (38) from the high nonlinearities,their response speed will be limited by the motion of such defects. These may also be formed by other means than light and this will clearly have implications on photoelastic, pyroelectric and piezoelectric effects as well. We point out that materials like polydiacetylenes may show appreciable quadrupolar pyroelectric effect (39). 

It has been known that alternating LB films consisting of two different amphiphiles have noncentrosymmetric structures, and therefore, are expected to provide piezoelectric, pyroelectric and nonlinear optical properties. Therefore, we prepared alternating LB films consisting of 5-(p-dodecyloxyphenyl)pyrazine-2-carboxylic acid (DOPC)... 

The bending piezoelectricity in drawn and polarized polymer films was studied in detail by Kawai (1) (1970). Kitayama and Nakayama (1971) reported a very high piezoelectricity in composite films of polymer (PVDF, nylon 11, PVC) and powdered ceramics (barium titanate, PZT) after poling. In the case of PVDF and nylon, the piezoelectric constant increase by a factor of 102 when the ceramics make up 50% of the volume. The pyroelectricity and optical nonlinearity of polarized PVDF films have been studied by Bergmann, McFee, and Crane (1971). 

Nonlinear Physics Coiurol of molecular archiicclure lo produce asymmetric viruciurv- wiih high non-linear coefficients, e.g. in electro-optics. pyroelectric deieeiors. or acousioeleciric devices. 

The electrical characterization of polar media is crucial to investigate their suitability for ferroelectric memories, piezo- or pyroelectric devices and many other ferroelectric applications (see Chapter 3). Optical characterization of polar media is fundamental to investigate their ser-vicability for electro-optic devices or applications in the field of nonlinear optics (see Chapter 4). Additionally there are intentions to characterize polar media with a combination of both, electrical and optical methods, such as to understand ferroelectric phenomena that are influenced by the action of light. 

Garrett CGB. Nonlinear optics, anharmonic oscillators, and pyroelectricity. IEEE J Quantum Electron 1968 QE-4(3) 70. 

Landolt-Bomstein Numerical Data and Functional Relationships in Science and Technology, III/ll, Elastic, Piezoelectric, Pyroelectric, Piezooptic, Electrooptic Constants, and Nonlinear Dielectric Susceptibilities of Crystals, Springer-Verlag, Berlin, 1979. 

A number of other polymeric solids have also been the subject of much interest because of their special properties, such as polymers with high photoconductive efficiencies, polymers having nonlinear optical properties, and polymers with piezoelectric, pyroelectric and ferroelectric properties. Many of these polymeric materials offer significant potential advantages over the traditional materials used for the same application, and in some cases applications not possible by other means have been achieved. 

Chapter V of this Handbook is entirely devoted to the potential applications of the side chain liquid crystal polymers, but it is interesting to mention here the main areas where FLCPs could play a role. As far as we know, the following applications can be considered for SmC LCPs nonlinear optics, pyroelectric detectors, and display devices. 

Polymers exhibit many unique properties which open up numerous technological opportunities in the fields of optics and electrooptics. They combine the possibility of easy processing with an infinite potential for functionalization. They can thus be ferroclectrics, conductors or semiconductors, mesomorphous and can exhibit photoconductivity, piezo or pyroelectricity or nonlinear optical properties. These polymers give rise to a tremendous number of potential applications such as optical data recording, optical communications, displays... 

Point group Enantiomorphism Pyroelectricity (vector property) Piezoelectricity, second-order optical nonlinearity (third ra/jA tensor property)... 

Landolt-Bomstein Numerictil Data tmd Functional Relationships in Science and Technology, New Series. Gn IB Crystal tmd Solid State Physics. Vol. 11. Revised and Extended Edition of Volumes 111/1 and 111/2. — Elastic, Piezoelectric, Pyroelectric, Electrooptic Consttmts, and Nonlinear Susceptibility of CrysUils, 854 p. Springer, Berlin/Heidelberg/New York (1979)... 

E. M. Savitskii, A. Prince Handbook of Precious Metals (Hemisphere, New York 1989) pp. 117-128 K.-H. Hellwege, A. M. Hellwege (Eds.) Elastics, Piezolelectric, Pyroelectric, Electrooptic Constants, Nonlinear Dielectric Susceptibilities of Crystals, Landolt-Biiistein, New Series 111/18 (Springer, Berlin, Heidelberg 1984) p.66 Doduco Datenbuch, Handbuch fur Techniker, 2. Aufl(Doduco, Pforzheim 1977)... 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

Like solid ferroelectrics, the ferroelectric liquid crystals, particularly the FLCPs, show a pyroelectric effect and a piezoelectric effect and are capable of switching polarization direction (dielectric hysteresis). Moreover, they can switch propagating or reflected polarized light. Finally, the polar symmetry of the phase leads to nonlinear optical properties of the FLCPs such as second-harmonic generation, the Pockels effect, and the Kerr effect. These physical properties of the ferroelectric LC polymers are discussed in the following sections. 

FLCPs can be used for many different applications, especially for electro-optic, thermo-optic, nonlinear optic, pieziolectric, or pyroelectric applications. In contrast to low-molar-mass FLCs, polymers have a much higher viscosity. This can be an advantage or a disadvantage for possible applications. Due to the high flow viscosity of the polymers, very simple flexible di.splays can be produced. The optical... 

Polar films made of polymer ferroelectrics can be used as pyroelectric radiation detectors [75], piezoelectric transducers, and nonlinear optical devices [76]. Another way to have the storage effect is to use the smectic A... 

In summary, chiral smectic-C phases lack a center of symmetry. Hence they can be used as materials for second-order nonlinear optics [120-124], and possess piezoelectric and pyroelectric properties. Pyroelectric measurements have been performed on LC polymers [125] as well as on LCEs [126-128]. Irradiation of an FLCE sample with light usually leads to a temperature increase resulting in a pyroelectric signal [129]. More interesting are systems in which dye molecules like azobenzenes lead to a shift of the phase transition temperature upon isomerization [19]. 

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-... 

---