Fig. 2.
The electrical conductivity of composite threads was improved under compression. a The electrical conductivity σ of both n-type and p-type threads were improved with increasing applied compression pressures p in a log-linear plot. b, c Log-log plots demonstrate an asymptotic power-law relation between conductivity and pressure at high pressures. For the pure theoretical power-law fit line (central gray dash) the volume fraction is equal to the critical value with power-law exponent s = 0.87 (0.90) for p- (n-) type threads according to modified percolation theory in Eq. 2. The downward trend of experimental data matches the fit lower gray dash curve, implying that the initial concentration is just below the percolation threshold for conduction Φ(0) < Φc. Conversely, if the conductivity were to saturate at low pressure (upper gray dash curves), this would imply that the initial concentration exceeded the percolation threshold Φ(0) > Φc.