Theoretical models of a.c. conductivity

The early conductivity model of Stevels (1957) and Taylor (1956, 1959) is in a sense a random potential energy model. It is assumed in this model that the ions experience randomly varying potential energy which is due to the presence of a random structure. For the d.c. conduction, the 

From this expression, if ai(co) and 02(00) are the conductivities of two solids, then at high frequency (co- 00), 

Since Ae differs only little for various solids, the a.c. conductivities of most solids differ very little at high frequency. 

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