Dielectric storage

FIGURE 13.24 (a) The dynamic mechanical spectrum for polyfethylene terephthalate) (PET) showing the storage modulus and tan 5 as a function of temperature, (b) The dielectric (storage and tan 5) behavior for PET in comparison with the mechanical response. (From Wetton, R.E. et al.. Inti. Lab., March, 1986. Figure 13a and Figure 13b, p. 60. With permission from International Laboratory.)... 

Figure 4a. Dielectric storage (s ) and loss (e") moduli vs. tempoature at different frequencies (1-100 Hz) for the as-received poly(amide-imide) with 2.5% water.

For non-magnetic conductive materials (i.e., = /i = x lo- H/m and ), the intrinsic impedance ti of snch materials is primarily dependent on the DC electrical conductivity o (Paul, 1992). The overall polarizability of the material can be expressed as a complex electrical permittivity, which accounts for the dielectric storage and losses (Ramo et al., 1984 Nanni and Valentini, 2011). Thus, in nanocomposites, whose conductivity is not high compared to pure metals (ie., 101 S/m vs. 107 S/m), the polarization loss e" also plays a role in determining the EM SE, primarily in the absorptive component of shielding, and can be viewed as another entropic effect (Ramo et al., 1984). 

Capacitors. Ceramic materials suitable for capacitor (charge storage) use are also dependent on the dielectric properties of the material. Frequently the goal of ceramic capacitors is to achieve maximum capacitance in minimum volume. The defining equation for capacitance is given by ... 

An alternative method of studying the molecular motions of a polymeric chain is to measure the complex permitivity of the sample, mounted as dielectric of a capacitor and subjected to a sinusoidal voltage, which produces polarization of the sample macromolecules. The storage and loss factor of the complex permitivity are related to the dipolar orientations and the corresponding motional processes. The application of the dielectric thermal analysis (DETA) is obviously limited to macromolecules possessing heteroatomic dipoles but, on the other hand, it allows a range of frequency measurement much wider than DMTA and its theoretical foundations are better established. 

A Ragone plot (Figure 7) compares the power and energy density of electrical energy storage devices. Electrolytic capacitors, based on an oxide dielectric, for example, arc associated with high-power densities... 

Fig. 1. Schematic of (a) conventional continuous floating gate CMOS memory and (b) nanocrystal CMOS memory. Discrete charge storage in nanocrystal memories reduces the possibility of charge loss through defects in the underlying tunnel dielectric. = floating gate = defect in tunnel oxide...

In storage capacitors it is important that we keep the dielectric constant to a minimum. This is not just a question of selecting the most appropriate polymer we must also ensure that contaminants that could raise the dielectric constant are kept to a minimum. Polymer manufacturers sell special grades of polypropylene (which is invariably the polymer of choice) that they describe as "ultraclean . These resins are made with catalysts that are extremely active and thus leave very little residue in the polymer. Such resins typically contain little or no anti-oxidant and are extruded under conditions and using equipment that are designed to minimize oxidation. 

Fig. 11. Effect of dielectric constant of dispersed particle on the ER effect in a polymer gel. The increment in shear storage modulus induced by an ac electric field of 0.4 kV/mm is plotted as a function of the real part of the dielectric constant of the particle...

The dielectric constant and breakdown field of a material are not the only considerations. Because a capacitor is used for charge storage, the leakage properties of the film are also critical. These are largely controlled by the defects in the films which can include oxygen (anion) vacancies or mixed valence effects in the cations. It is important that films that are as fully oxidized as possible be studied. 

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