Nonlinear Conductivity and Permittivity Spectra of Ion Conducting Glasses

Abstract

Abstract We have measured third-order conductivity and permittivity spectra of a Li2O · Al2O3 · 4 SiO2 glass and of a 0.15 Na2O · 0.85 GeO2 glass by applying ac electric fields up to 100 kV cm−1. For the application of these high fields, the glass samples are interfaced with highly conductive liquid electrolyte solutions. In this field range, the electrical response due to ion dynamics in the bulk of a glass sample is weakly nonlinear, while the electrical reponse due to ion transport across the interface between glass sample and liquid electrolyte is strongly nonlinear. For both glasses, the real part of the third-order conductivity is characterised by a change in sign in a frequency range where the diffusive bulk ion dynamics passes over into the subdiffusive bulk ion dynamics. On the other hand, the real part of the third-order permittivity spectra is characterised by a change in sign at lower frequencies where ion transport across the glass / liquid electrolyte interface passes over into the bulk ion transport. We show that these changes in sign can be rationalised by considering an equivalent circuit for a disordered solid ion conductor interfaced with a highly conductive liquid. In this circuit, the bulk and interfacial resistances are assumed to decrease with increasing voltage.