A new experimental system has been developed, which enables measuremen
ts of linear as well as non-linear complex conductivities to be made.
The frequency dependence of linear to fifth-order non-linear complex c
onductivities at different temperatures in a polyethylene oxide/salt c
omplex can then be measured. A characteristic conduction relaxation ph
enomenon was observed in the spectra, which suggested the existence of
different ion-conduction mechanisms between the high- and low-frequen
cy regions. It was also found that the ratio of linear to non-linear c
onductivities was closely related to the elementary process of ionic t
ransport. Furthermore, this ratio obtained from non-linear measurement
s allowed an estimate of the important parameters which characterized
ionic transport in ion-conducting polymers, such as the hopping distan
ce of an ion or the size of a connected cluster of the site capable of
ion hopping, without the need for any additional assumptions. Thus, i
t was found that in a polyethylene oxide/salt complex, the typical siz
e of a connected cluster of the effective sites capable of ion hopping
was approximately 4 nm.