Dielectric Response
Nearly all materials are dielectrics, and the measurement of their dielectric response is a very common technique for their characterisation. This chapter is intended to guide scientists and engineers through the subject to the point where they can interp
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Dielectric Res 10. Dielectric Response
Nearly all materials are dielectrics, that is they do not exhibit a direct-current (DC) conductivity on the macroscopic scale, but instead act as an electrical capacitance i. e. they store charge. The measurement of the dielectric response is noninvasive and has been used for material characterisation throughout most of the 20th century, and consequently a number of books already exist that cover the technique from various points of view. Those that have stood the test of time are Debye [10.1], Smyth [10.2], McCrum et al. [10.3], Daniels [10.4], Bordewijk and Bottcher [10.5], and Jonscher [10.6]. These texts cover the subject in terms of the basic physics [10.1, 5], the material properties [10.2–4], and the electrical features [10.6]. An introduction to the wide range of dielectric response measurements that are undertaken can be obtained by referring to the proceedings
10.1
Definition of Dielectric Response........... 10.1.1 Relationship to Capacitance ....... 10.1.2 Frequency-Dependent Susceptibility ............................ 10.1.3 Relationship to Refractive Index .
188 188 188 189
10.2 Frequency-Dependent Linear Responses 190 10.2.1 Resonance Response ................. 190 10.2.2 Relaxation Response ................. 192 10.3 Information Contained in the Relaxation Response .................. 10.3.1 The Dielectric Increment for a Linear Response χ0 ............ 10.3.2 The Characteristic Relaxation Time (Frequency)....................... 10.3.3 The Relaxation Peak Shape.........
196 196 199 205
10.4 Charge Transport ................................. 208 10.5 A Few Final Comments ......................... 211 References .................................................. 211
readers can choose for themselves how far to rely on them.
publication of the International Discussion Meeting on Relaxations in Complex Systems [10.7]. In view of the enormous range of properties and materials covered by the topic it is not feasible or desirable to attempt to review the whole field in a chapter such as this. Instead the topic is approached from the viewpoint of a researcher who, having measured the dielectric spectrum (i. e. frequencydependent complex permittivity) of a material sample, wishes to know what information can be taken from the measurements. Along the way the limits on the information content and the problems (and controversies) associated with the microscopic and molecular-scale interpretation will be identified. Emphasis will be placed on the physical concepts involved, but inevitably there will be some mathematical expressions whose features I aim to place in as simple a physical context as possible.
Part A 10
Nearly all materials are dielectrics, and the measurement of their dielectric response is a very common technique for their characterisation. This chapter is intended to guide scientists and engineers through the subject to the point where they can interpret their data in terms of the microscopic and atomistic dynamics responsible for the dielectric res
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