Optical and Dielectric Properties

The dielectric constant of a medium is the constant of proportionality in the relation between the dielectric displacement and the strength of the electric field. The polarization of the medium is given by 

Reorientation of dipoles in the direction of the field is characterized by a relaxation time, T. When t is small compared to the frequency of the applied voltage, instantaneous polarization occurs when t is large, the resultant polarization will be free from orientational contribution. A dispersion of polarization and hence of e, occurs when the frequency and t are close to each other and e, in this region is a complex quantity, — i . In the region of dispersion there is a phase lag between the applied field and the instantaneous polarization when the phase angle 5 is small, tan 5 = eJe,. Furthermore, 

and are the static (low-frequency) and optical (high-frequency) dielectric constants respectively. 

When (Na/3e ) = 1, both polarization and susceptibility go to infinity. At a critical temperature, T, the randomizing effect of temperature is balanced by the orienting effect of the internal field. Under such conditions, Xe is given by the Curie-lVeiss law 

The behaviour of dielectrics in alternating electric fields may be treated in the framework of forced harmonic oscillation. The displacement is then given by 

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Processes such as film extrusion, fiber spinning, injection molding, and drawing tend to impart orientation to products made from semicrystalline polymers. Mechanical, dielectric, and optical properties, to mention only three, are often strongly influenced by orientation. X-ray diffraction offers a direct approach to studying crystallite orientation because the Intensity that is diffracted into a detector placed at an appropriate position is directly proportional to the number of crystal lattice planes that are in the correct orientation for diffraction. The principles of such measurements are well described in textbooks 0,2). 

When a strong static electric field is applied across a medium, its dielectric and optical properties become anisotropic. When a low frequency analyzing electric field is used to probe the anisotropy, it is called the nonlinear dielectric effect (NLDE) or dielectric saturation (17). It is the low frequency analogue of the Kerr effect. The interactions which cause the NLDE are similar to those of EFLS. For a single flexible polar molecule, the external field will influence the molecule in two ways firstly, it will interact with the total dipole moment and orient it, secondly, it will perturb the equilibrium conformation of the molecule to favor the conformations with the larger dipole moment. Thus, the orientation by the field will cause a decrease while the polarization of the molecule will cause an... 

It should be noted that dielectric and optical properties of the near-the-surface layer of a semiconductor, which vary in a certain manner under the action of electric field, depend also on the physicochemical conditions of the experiment and on the prehistory of the semiconductor sample. For example, Gavrilenko et al (1976) and Bondarenko et al. (1975) observed a strong effect of such surface treatment as ion bombardment and mechanical polishing on electroreflection spectra. The damaged layer, which arises in the electrode due to such treatments, has quite different electrooptic characteristics in comparison with the same semiconductor of a perfect crystalline structure (see also Tyagai and Snitko, 1980). 

The measured enthalpies of adsorption of alkanes into zeolites are very large, and can be calculated from this formula [13]. The dielectric constants for the open networks formed by the aluminium silicate frameworks of zeolites can be related to the known and measured dielectric and optical properties of bulk quartz. The calculation assiunes that the zeolite framework tessellates a hyperbolic surface as described in Chapter 2. The polarisabilities of different adsorbate alkanes are also known. When the calculations are carried out for a whole range of alkanes as adsorbate molecules and for different zeolites (with differing pore structure and size) the agreement between measured and predicted heats of adsorption is excellent (cf. Fig. 3.2). The results depend... 

Diffusion of small impurity molecules is an important issue of polymers particularly with respect to their mechanical, dielectric, and optical properties as well as ageing, and has stimulated extensive theoretical and experimental work within the past years [90,91], Diffusion in amorphous polymers is often random on a macroscopic scale, this must not necessarily... 

Evidence exists that a second tetragonal phase also exists with a cristobalite crystal type. No distinction was found in the literature for the dielectric and optical properties of the two monomorphs. 

Kamzina LS, Wei R, Zeng JT, Li GR (2011) Effect of the La concentration on the dielectric and optical properties of the transparent ferroelectric ceramics 75PbMgi/3Nb2a03-25PbTi03. Phys Solid State 53 1608-1613... 

Tsurumi, T., Ichikawa, X, Harigai, X, Kakemoto, H., Wada, S. Dielectric and optical properties of Ba1i03/SrXi03 and BaXiOs/BaZiOs superlattices. J. Appl. Phys. 91, 2284-2289 (2002)... 

The first exact expression of this type was derived by Maxwell [1881] for the dc conductivity of a dispersion of spheres in a continnons medinm. Maxwell Garnett [1904] derived a similar expression for dielectric and optical properties. Wagner [1914] extended Maxwell s model to the complex domain and this model has thereafter been known as the Maxwell-Wagner model. It gives the following expression for complex conductivity ... 

Sonntag B (1976) Dielectric and optical properties. In Klein ML, Venables JA (eds) Rare gas solids, vol 1. Acad Press, London... 

It is claimed to be able to measure thicknesses with an accuracy of about 0.3 A, approximately the thickness of an atomic layer. Because the method relies on polarized fight, ellipsometry is a nondestructive technique, which makes it suitable for in situ measurements in some cases. One disadvantage is that the substrate must be reflective, so gold or sUicon wafer is often used. However, a major disadvantage with the technique is interpretinging the data, which is not trivial models of the air—thin film-substrate must be used. The dielectric and optical properties of the thin film must be known accurately to calculate the thickness of the film, and even then the modelling usually assumes a homogeneous layer which may not always be justified. 

Borrelli NF, Layton MM (1971) Dielectric and optical properties of transparent ferrorelectric glass-ceramic systems. J Non-Cryst Solids 6(3) 197-212... 

These side compounds caused defects in the s)mthesized PI film. They are unwanted impurity in production of nanostructured films with chromophores as a "guest" in the matrix, since they lead to low quality of dielectric and optical properties of layers. At... 

Carl, K., Geisen, K. (1973). Dielectric and optical properties of a quasi-ferroelectric PLZT ceramic. Proc, IEEE, Vol. 61, No. 7, pp. 967-974. 

Although the solvent-reorganisation expression (9.10) has been derived purely from electrostatic theory, there is some direct experimental support for the implied dependence of AG j. on the dielectric and optical properties of the solvent. This comes from rate measurements (by nmr line-broadening) on some self-exchange electron-transfer reactions where one of the reactants is neutral, such as the ruthenium-complex system (L = hexaflu-oroacetylacetonate) [6,a] ... 

Bagshaw S.A., Prouzet E., Pinnavaia T.J. Templating of mesoporous molecular sieves by nonionic polyethylene oxide surfactants. Science 1995 269 1242-1244 Balkenende A.R., de Theije F.K., Kriege J.C.K. Controlling dielectric and optical properties of... 

Sonntag, B., 1977, Dielectric and optical properties, irii "Rare Gas... 

At present, the major focus of the researchers is on the nanocomposite materials based on the nanoparticles of metals and their compounds stabilized within a polymeric dielectric matrix [1-4]. The dielectric and optical properties of these materials have been demonstrated to be highly dependent on the size, structure, and concentration of the nanopartides, as well as on the type of polymeric matrix [5-8]. These have shown the possibility of the purposeful change of parameters of the nanocomposite materials such as electrical conductivity, complex permittivity, refraction coefficient, and so on. It is believed that these materials would demonstrate low acoustic impedance because they are based on the polymeric matrix [9]. At that, the impedance value should be varied within certain limits by adjusting the parameters of the embedded nanopartides. All of these would allow one to use these materials for low disturbing substrates in various devices based on the waves in thin piezoelectric plates [10]. 

Malik MK, Deshmukh RR (2014) Electro-optics of homogeneously aligned nematic liquid crystals stabilized by a polymer network. Int J ChemTech Res 6 1833-1835 Manohar R, Tripathi G, Singh AK, Srivastava AK, Shukla JP, Prajapati AK (2006) Dielectric and optical properties of polymer-liquid crystal composite. J Phys Chem Solids 67 2300-2304 Mei E, Higgins DA (1998) Polymer-dispersed liquid crystal films studied by near-field scanning optical microscopy. Langmuir 14 1945-1950... 

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