Previous I _o vs. $\sigma$ Data

The direct relationship between the initial RCT current I _o and sample conductivity established in this experiment is in contrast to results reported elsewhere. Hansen et al. [32] reported both the initial current and the AC impedance at 1 kHz. However, their data showed that, for a given specimen, the AC impedance was considerably greater than the resistance calculated from the initial current. This may be explained using the IS data for the RCT cell that is shown in Fig. 3. The real component of the total impedance at 1 kHz is greater than R_B. Also, if the apparatus used in the experiment by Hansen et al. reported the magnitude of the impedance ($\vert Z\vert = \sqrt{Z'^2+Z''^2}$), the difference is accentuated by the greater contribution by Z" at 1 kHz than at Z ' = R_B. However, the general relationship between initial current and charge passed expressed in Table 7 of Hansen et al. agree with the results reported here.

The experiments reported by Feldman and coworkers [20, 21] also included measurements of specimen impedance and RCT initial current. The impedance measurements were conducted at 10 kHz. However, calculations of specimen resistivity using their RCT initial current differ from the IS measurements by 20 % or more in most cases. The source of the discrepancy cannot be explained given the results reported herein since the real component of Z at 20 kHz reported here in Table 4 is typically within a few percent of R_B .