Permittivity components, temperature dependence

From the value of the resonant frequency and its change with temperature or other external parameters the permittivity of a dielectric sample and its temperature or field dependence can be determined. In case of superconductors, the temperature dependence of the magnetic field penetration depth can be determined [8], Since the mode spectrum of a resonator is controlled both its physical dimensions and by the material properties, the physical dimensions of all resonator components have to be known with tight tolerances. Relative changes of permittivity or penetration depth can be determine with much higher accuracy than absolute values. 

This anisotropy, illustrated by refractive index, extends to other properties, and common properties of interest would be the anisotropy in linear polarizability (Aa), dielectric permittivity (Ae), and diamagnetism (Ax). In the nematic phase, these properties are quite strongly temperature dependent the order parameter, S, increases as samples cool away from the N-I transition. This is illustrated in Figure 19 where it is also seen that the parallel component has the stronger temperature dependence as it is the orientational correlations that increase on cooling. 

Dielectric spectroscopy is concerned with the dependence of complex permittivity on temperature and frequency. The relatively low level of d.c. conduction in polycarbonate ensures that the principal relaxations associated with polycarbonate s active C 0 dipole can be observed over a useful range of frequency and temperature. In multi-phase or multi-component polymers charge accumulation at the sub-structure interfaces leads to Maxwell-Wagner-Sillars (MWS) contributions to the overall polarization. 

Fig. 1. Temperature dependences of the principal components of the electric permittivity tensor in monomer and fully polymerized pTS (e ). The numbers correspond to the indices of the components, the symbols "M and "P" refer to monomer and polymer, respectively. Results obtained for pFBS are also shown for comparison curves "A" and "B" refer to the measurements carried out along the a and b directions of pFBS, respectively. Note the different scales of e in Figs, la and lb.

Figure 6.4. Generic behavior of temperature dependence of permittivity components (e, 8") recorded for an amorphous polymer with considerable ionic conductivity. The higher the relaxation time of the mechanism, the higher the temperature range at which the corresponding signal appears in this isochronal recording. The signals present in this spectrum will shift to lower temperatures by decreasing the frequency of the alternating electric field.

For other substances the parallel permittivity component, e,, is only known. Figure 11 shows a typical behavior of the static permittivity e n in the nematic and isotropic phase of 7PCH at constant temperatures, while the pressure was successfully reduced from the points close to the nematic-solid transition line. Figure 12 presents the dependencies of e, on the reduced pressure, p —Pni, for different substances studied. It is... 

Note that a fraction of the quantum-mechanical component of the medium polarization, i.e. the polarization satisfying the condition ho) kT, slowly decreases with increasing temperature. This, as well as the temperature dependence of permittivities mentioned above, does not allow us to consider Eg as constant over a very wide range of temperatures. 

In mixed solvent, CCI4-C6H5CI, universal relation to acetic acid (because the mixed solvent components do not enter into specific solvation with the acid), the dimerization constant dependence on the temperature and permittivity in accordance with [9.52.a] and [9.56] is described by equation ... 

In the following discussion it should be noted that we use the same symbol, s, to represent both mechanical strain and the electrical dielectric constant. This is based on common terminology from the literature and should not cause the reader any difficulty, since both are used in differing contexts, s represents the complex dielectric constant, s the in-phase component or permittivity, and e" the out-ofphase component or dielectric loss factor. It is also important to note that the dielectric constant is not a constant but is strongly dependent on both frequency and temperature. 

The temperature and pressure dependence of the parallel component of the static permittivity, e, was studied for several n-alkylcyanobiphenyls (SCB, - 6CB, 7CB, and 8CB ), as well as for other similar compounds (6CHBT, 5PCH, 7PCH, 80CB, and 5CCH ). However, the perpendicular component, and the dielectric anisotropy, Ae, are known for 5CB and 6CB only. ... 

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