The Dielectric Properties of Insulating Materials 



By E. J. MURPHY and S. O. MORGAN 



This paper gives a qualitative account of the way in which 

 dielectric constant and absorption data have been interpreted in 

 terms of the physical and chemical structure of materials. The 

 dielectric behavior of materials is determined by the nature of the 

 polarizations which an impressed field induces in them. The 

 various types of polarization which have been demonstrated to exist 

 are listed, together with an outline of their characteristics. 



I. Outline of the Physico-Chemical Interpretation 

 OF THE Dielectric Constant 



THE development of dielectric theory in recent years has been 

 along such specialized lines that there is need of some correlation 

 between the newer and the older theories of dielectric behavior to 

 keep clear what is common to both, though sometimes expressed in 

 different terms. The purpose of the present paper is to outline in 

 qualitative terms the way in which the dielectric constant varies with 

 frequency and temperature and to indicate the type of information 

 regarding the structure of materials which can be obtained from the 

 study of the dielectric constant. 



The important dielectric properties include dielectric constant (or 

 specific inductive capacity), dielectric loss, loss factor, power factor, 

 a.c. conductivity, d.c. conductivity, electrical breakdown strength and 

 other equivalent or similar properties. The term dielectric behavior 

 usually refers to the variation of these properties with frequency, 

 temperature, voltage, and composition. 



In discussing the dielectric properties and behavior of insulating 

 materials it will be necessary to use some kind of model to represent 

 the dielectric. The success of wave-mechanics in explaining why 

 some materials are conductors and others dielectrics suggests that it 

 might be desirable to use a quantum-mechanical model even in a 

 general outline of the characteristics of dielectrics, but for the aspects 

 of the theory of dielectric behavior with which we are immediately 

 concerned here the behavior predicted is essentially the same as that 

 derived on the basis of classical mechanics. However, in the course 

 of the description of the frequency-dependence of dielectric constant 

 we shall have occasion to make a comparison between the dispersion 



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