Dielectric constant solids

A Mott-Wannier exciton is a neutral quasi-particle, consisting of an excited bound-state electron and its associated "Coulomb hole" in a high-dielectric constant solid, that can also travel throughout the lattice without transporting net charge since the exciton radius is several lattice constants, its binding energy is as low as 0.01 eV it thus tends to be more "delocalized" than the Frenkel exciton. 

The dielectric constant is concerned with the electrical properties of a material. The dielectric constant for a solid is a 3 x 3 matrix with different components according to the Cartesian axes. These elements are given by ... 

Tetralluoroethylene polymer has the lowest coefficient of friction of any solid. It has remarkable chemical resistance and a very low brittleness temperature ( — 100°C). Its dielectric constant and loss factor are low and stable across a broad temperature and frequency range. Its impact strength is high. 

Alkaline-Earth Titanates. Some physical properties of representative alkaline-earth titanates ate Hsted in Table 15. The most important apphcations of these titanates are in the manufacture of electronic components (109). The most important member of the class is barium titanate, BaTi03, which owes its significance to its exceptionally high dielectric constant and its piezoelectric and ferroelectric properties. Further, because barium titanate easily forms solid solutions with strontium titanate, lead titanate, zirconium oxide, and tin oxide, the electrical properties can be modified within wide limits. Barium titanate may be made by, eg, cocalcination of barium carbonate and titanium dioxide at ca 1200°C. With the exception of Ba2Ti04, barium orthotitanate, titanates do not contain discrete TiO ions but ate mixed oxides. Ba2Ti04 has the P-K SO stmcture in which distorted tetrahedral TiO ions occur. 

Figure 9-26. Expcrimenial and calculated (solid lines) UV characteristics of ITO/PPV/Au hole-only devices of various thicknesses, L. The current flow in all devices is described by SLC with a hole mobility //, = 1(r cm2 V"1 s 1 and with a dielectric constant of 3. The inset shows the chemical structure of the PPV investigated in that study (R =CHi, R2=CiUH2i). Reproduced from Ref. 185).

Capacitive Sensors. This device usually consists of a capacitor which is formed either from two concentric cylinders or from a pair of parallel plates. The solid sample to be analyzed for moisture content is passed between these plates. Since w has a large dielectric constant, the w content of the sample causes a significant change in the dielectric constant of the solid, which is measured using bridge or frequency techniques. 

The variations of dielectric constant and of the tangent of the dielectric-loss angle with time provide information on the mobility and concentration of charge carriers, the dissociation of defect clusters, the occurrence of phase transitions and the formation of solid solutions. Techniques and the interpretation of results for sodium azide are described by Ellis and Hall [372]. 

It is predicted that the dielectric constants of solid HC1, HBr, and HI at temperatures just below the melting points will be very high and dependent on the temperature, the values being given by Debye s theory of the orientation of electric dipole molecules while the low-temperature forms will have low dielectric constants nearly independent of the temperature. 

Fig. 1. Plots of dielectric constant vs selectivity of bromination of phenol with Br2 (left) and NBS (solid powder) (right). ort/io-Bromophenol (A), para-Bromophenol ( ).

The liquid-liquid interface is not only a boundary plane dividing two immiscible liquid phases, but also a nanoscaled, very thin liquid layer where properties such as cohesive energy, density, electrical potential, dielectric constant, and viscosity are drastically changed along with the axis from one phase to another. The interfacial region was anticipated to cause various specific chemical phenomena not found in bulk liquid phases. The chemical reactions at liquid-liquid interfaces have traditionally been less understood than those at liquid-solid or gas-liquid interfaces, much less than the bulk phases. These circumstances were mainly due to the lack of experimental methods which could measure the amount of adsorbed chemical species and the rate of chemical reaction at the interface [1,2]. Several experimental methods have recently been invented in the field of solvent extraction [3], which have made a significant breakthrough in the study of interfacial reactions. 

The Gouy-Chapman theory relates electrolyte concentration, cation valence, and dielectric constant to the thickness of this double layer (see Equation 26.2). This theory was originally developed for dilute suspensions of solids in a liquid. However, experience confirms that the principles can be applied qualitatively to soil, even compacted soil that is not in suspension.5... 

K = 2 (typical dielectric constant for insulating solid in fluidized state)... 

The rotation angle between the two planar pyridyl-rings was found to vary between 18.2 (solid-state [293]) and 37.2 (gas-phase [294]). H-NMR experiments in several solvents of different dielectric constants revealed that 4,4 -BP appears either highly twisted, or as a free rotor. The barrier to internal rotation has been estimated to be 17.0 kJ mol-1. The two rings are rotating almost freely in most liquid environments [295-297]. 

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