Solids, dielectric properties

Figure C2.17.13. A model calculation of the optical absorjDtion of gold nanocrystals. The fonnalism outlined in the text is used to calculate the absorjDtion cross section of bulk gold (solid curve) and of gold nanoparticles of 3 mn (long dashes), 2 mn (short dashes) and 1 mn (dots) radius. The bulk dielectric properties are obtained from a cubic spline fit to the data of [237]. The small blue shift and substantial broadening which result from the mean free path limitation are...

Fig. 1. Effect of compositional variations on the dielectric properties of strontium titanate-barium titanate solid solutions. A, BaQ SrQ QTiO B,...

Hoffmann, S. Waser, R. M. 1997. Dielectric properties, leakage behavior, and resistance degradation of thin films in the solid solution series Ba(Tii yZry)03. Int. Ferro. 17(1-4) 141-152. 

Another important group of oxide materials with a very low electrical conductivity is the oxide dielectrics. A number of these are based upon the perovskites, MXO3 or M0 X02. The archetype of these materials is BaTiC>3, which has a high dielectric constant, or relative permittivity to vacuum, the value at room temperature being 1600, and commercial use is made of the isostructural PbTi(>3 and ZrTi03 which form solid solutions, the PZT dielectrics. These materials lose their dielectric properties as the temperature... 

Water absorption can also cause significant changes in the permittivity and must be considered when describing dielectric behavior. Water, with a dielectric constant of 78 at 25°C, can easily impact the dielectric properties at relatively low absorptions owing to the dipolar polarizability contribution. However, the electronic polarizability is actually lower than solid state polymers. The index of refraction at 25°C for pure water is 1.33, which, applying Maxwell s relationship, yields a dielectric constant of 1.76. Therefore, water absorption may actually act to decrease the dielectric constant at optical frequencies. This is an area that will be explored with future experiments involving water absorption and index measurements. 

The study of the effect of electric fields on the properties of solids dates back to Zener s (1934) investigation of electrical breakdown in solid dielectrics. Further pioneering work was carried out by Houston (1940) and Slater... 

One aspect of the research will examine equilibrium aspects of solvation at hydro-phobic and hydrophilic interfaces. In these experiments, solvent dependent shifts in chromophore absorption spectra will be used to infer interfacial polarity. Preliminary results from these studies are presented. The polarity of solid-liquid interfaces arises from a complicated balance of anisotropic, intermolecular forces. It is hoped that results from these studies can aid in developing a general, predictive understanding of dielectric properties in inhomogeneous environments. 

Solid food materials have dielectric properties dependent upon their composition. In many instances, particularly when developing microwavable food products, it is necessary to know the effective bulk microwave properties of the product, crushed, as is, or when agglomerated together. Typical examples are peas, beans, com, pasta, flour... 

Mudgett, R., Goldblith, S., Wang, D., and Westphal, W. 1977. Prediction of dielectric properties in solid food of high moisture content at ultrahigh and microwave frequencies. Journal of Food Processing and Preservation 1 119-151. 

Dielectric measurements have been established for nearly three decades as a technique for monitoring the cure of polymeric resins. Dramatic changes in the dielectric properties of the material accompany the transformation of the resin from a viscous liquid to a solid. 

Constant-phase elements were first used to explain dielectrical properties of polar liquids and solids, and were attributed to the presence of the investigated material properties as a partitioning between extreme conditions, rather than as constant or uniform parameters40. Furthermore in the... 

Theoretical considerations by Clarke and co-workers (Clarke, 1987 Clarke etal., 1993) show that an equilibrium film thickness arises from the competition between attractive dispersion forces determined by the dielectric properties of the grains and repulsive disjoining forces which can be steric forces and/ or double-layer forces. Wetting will occur when the solid-solid boundary energy, yb, is less than that of the wetted boundary, 2y, where y is the liquid-solid interfacial energy (Clarke, 1985), provided that there is a suitable source of liquid, for example as a consequence of liquid-phase sintering at high temperatures. 

Masking of the Van der Waals forces. By choosing a suspending medium with dielectric properties as close as possible to those of the solid (particularly at optical and UV frequencies), the van der Waals force is minimised. 

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