Dielectric Relaxation Spectroscopy
نویسنده
چکیده
C.M. Roland (December 17, 2014) Introduction Impedance spectroscopy and dielectric relaxation measurements yield the same information; however, their purpose and analysis methods differ. Impedance spectroscopy is typically used to probe electrochemical processes, while dielectric relaxation data, almost invariably expressed in the complex permittivity representation, provide information on dynamical processes, typically the rate of molecular or polymer chain reorientation. Moreover, the features of interest in an impedance measurement, such as the transport and adsorption of charges, are an unwanted contribution to dielectric relaxation spectra, and thus are either ignored or removed from the latter. (Occasionally, the impedance function representation is used to eliminate interferences with relaxation measurements.) Since the objective of dielectric spectroscopy is to characterize the dynamics, models of molecular motion are the basis for interpretation; equivalent circuits, prominent in impedance spectroscopy studies, are not employed to analyze relaxation spectra. However, since relaxation spectra can be described formally as a distribution of exponential relaxation processes [1,2], an equivalent circuit diagram can be constructed (Figure 1 [3]). Such a description is phenomenological (a mathematical convenience), and its underlying premise, that the observed peak shape reflects a distribution of exponential decays, is problematic [4,5]. Table 1 summarizes the distinct aspects of impedance and dielectric relaxation spectroscopies.
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