E. Gutman and G. Hartmann (G-H) have published a study on the electrical conductivity of two component developer materials. The carriers used in conductive developers typically have a metal core surrounded by an oxide layer that, in turn, may be partially covered by a polymer coating. G-H found that either a Schottky model or a Poole-Frenkel model could describe the current through the developer material in the nip of a magnetic brush. Both models have an exponential dependence on the applied electric field or voltage. For low voltages or electric fields, deviations from the exponential voltage dependence were observed as the developer conductivity decreased due to increasing toner concentration. The deviations were reminiscent of contact resistance effects observed with thin film I-V measurements. The analysis of the developer I-V data is consistent with a contact barrier between the electrodes and the developer sample.
E.J. Gutman, K. Stamp, "A Possible Electrode Effect on the Measurement of the Conductivity of Two-Component Xerographic Developers" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP16), 2000, pp 583 - 587, https://doi.org/10.2352/ISSN.2169-4451.2000.16.1.art00042_2