We measured the ac conductivity and dielectric constant of a three-dimensional randomly mixed conductor-insulator system consisting of amorphous carbon and Teflon powder in the frequency range from 10 Hz to 13 MHz. Near the percolation threshold, these two quantities varied as a power of ω, such as σ∼${\omega }^x$, and ε∼${\omega }^{\mathrm{-}y}$. The values of x and y were found to be 0.86±0.06 and 0.12±0.04, respectively. These values are compared to the present percolation theories. We also measured the dc conductivity exponent t and dielectric constant exponent s to complete the study. Our data yielded t=1.85±0.25 and s=0.68±0.05.

• Received 17 July 1985

DOI:https://doi.org/10.1103/PhysRevB.33.904