Application of Nonlinear Conductivity Spectroscopy to Ion Transport in Solid Electrolytes

TL;DR

This study employs nonlinear conductivity spectroscopy to analyze ion transport in solid electrolytes, revealing larger-than-expected jump distances and challenging existing models of field-dependent ion movement.

Contribution

It introduces a method to accurately measure higher-order conductivity coefficients, demonstrating that traditional calculations of jump distances are physically inadequate.

Findings

Higher harmonics indicate field-dependent ion transport.

Apparent jump distances are larger than literature values.

Traditional models do not accurately describe ion transport under electric fields.

Abstract

The field-dependent ion transport in thin samples of different glasses is characterised by means of nonlinear conductivity spectroscopy. AC electric fields with strengths up to 77 kV/cm are applied to the samples, and the Fourier components of the current spectra are analysed. In the dc conductivity regime and in the transition region to the dispersive conductivity, higher harmonics in the current spectra are detected, which provide information about higher--order conductivity coefficients. Our method ensures that these higher--order conductivity coefficients are exclusively governed by field--dependent ion transport and are not influenced by Joule heating effects. We use the low-field dc conductivity $\sigma_{1,dc}$ and the higher--order dc conductivity coefficient $\sigma_{3,dc}$ to calculate apparent jump distances for the mobile ions, $a_{\rm app}$. Over a temperature range from 283 K to 353 K, we obtain values for $a_{app}$ between 39 \AA $ $ and 55 \AA . For all glasses, we find a weak decrease of $a_{\rm app}$ with increasing temperature. Remarkably, the apparent jump distances calculated from our data are considerably larger than typical values published in the literature for various ion conducting glasses. These values were obtained by applying dc electric fields. Our results provide clear evidence that the equation used in the literature to calculate the apparent jump distances does not provide an adequate physical description of field-dependent ion transport.