Concentration-Dependent Exponent for a.c. Hopping Conductivity and Permittivity
Th Robin, Bernard Souillard · Europhysics Letters (EPL) · 1993
We consider a composite medium made of grains in a dielectric matrix with hopping conduction between grains. We are interested in the a.c. conductivity σ(ω) or in the dielectric permittivity of the composite ε(ω) where ω is the frequency of the incident wave. We show for the first time that, near the percolation threshold, ε(ω) ∼ ω −y where the exponent y depends on the concentration of inclusions. Recent experimental results seem to back up this effect. We also discuss the dependence of y on temperature.