Nonlinear DC and Dispersive Conductivity of Ion Conducting Glasses and Glass Ceramics

Abstract

Abstract Frequency-dependent third-order conductivity spectra σ 3 ´(ν) of various ion conducting glasses and glass ceramics were obtained by applying sinusoidal electric fields with high amplitudes and by analysing the resulting higher-harmonic currents. In the DC conductivity regime, the third-order conductivity σ 3, dc was found to be positive for all materials and at all temperatures. From the ratio of the third-order conductivity to the low-field conductivity, σ 3, dc/σ 1, dc, apparent jump distances were calculated. These apparent jump distances are much larger than jump distances between neighbouring sites in the glasses and decrease with increasing temperature. In (Li2O)1-x ·(Na2O) x ·Al2O3·(SiO2)4 glasses, the mixed alkali effect leads to a minimum in the apparent jump distance, while partial crystallisation of Li2O·Al2O3·(SiO2)2 glasses leads to an increase of the apparent jump distance. In the dispersive regime, the third-order conductivity σ 3 ´(ν) of all glasses and glass ceramics is negative and exhibits an approximate power-law dependence, however with a larger exponent than the dispersive low-field conductivity σ 1 ´(ν). For a given material, the third-order conductivity spectra σ 3 ´(ν) obey the time–temperature superposition principle and can be superimposed by using the Summerfield scaling. Remarkably, the shift between the σ 3 ´(ν) master curves of different materials is much stronger than the shift between the σ 1 ´(ν) master curves. In order to rationalize this effect, we calculate the nonlinear dispersive hopping conductivity in a double minimum potential approximation.