Direct Current Conductivity of Thin-Film Ionic Conductors from Analysis of Dielectric Spectroscopic Measurements in Time and Frequency Domains

Abstract

A method is developed for extracting the direct current conductivity (σdc) of ion-conducting materials from frequency- and time-domain dielectric spectroscopy measurements. This method exploits the electrode polarization effects arising from the charging of an ion-blocking capacitor and provides a useful way of obtaining σdc for ionic conductors that do not exhibit a frequency- (time-) independent conductivity plateau; the latter absence of plateau is often encountered in the case of thin-film materials. It allows, by proper design of the test cells, the estimation of σdc independently of the specimen thickness, as demonstrated herein for SiO2 blocking layers and electrolyte systems made of a polyoxometalate (POM) molecule embedded in poly­(methyl methacrylate) (PMMA) polymeric matrices. For different postpreparation and measurement conditions, the σdc values obtained for thick (8 μm) POM–PMMA layers are in good agreement not only with the observed conductivity plateaus but also with the values determined in the case of thin (270 nm) POM–PMMA layers for which no plateau is detected. The proposed method allows for the probing of a possible dependence of material properties on thickness and is of substantial interest for low-dimensional systems. The applicability and accuracy of the method are discussed and assessed in relation to the main methods currently used in the field.