Volume low-frequency dispersion in a semi-insulating system

The phenomenon of low-frequency dispersion (LFD) is observed in semi-insulating solids in which slowly mobile electronic or ionic charge carriers dominate the dielectric response at low frequencies giving rise to very high effective capacitance values. This behavior may be associated with electrochemical activity. An experiment is described that was designed to answer the question of whether LFD may be associated with volume processes or whether it is essentially confined to interfacial activity. The investigators used the medium of humid cellulose in the form of sheets of filter paper soaked in a salt solution to provide ionic charge carriers. A stack of such filter papers sandwiched between metal electrodes, which may be regarded as representative of many others, gives volume LFD response distributed throughout the system, with only relatively negligible contributions from the end-electrode interfaces. While this does not rule out the existence of other interfacial LFD phenomena, it proves the existence of distributed volume LFD processes in ionically conducting systems