Ionic Transport in Glassy Networks with High Electronic Polarizabilities:  Conductivity Spectroscopic Results Indicating a Vacancy-Type Transport Mechanism

Abstract

We have carried out ac conductivity measurements on different alkali tellurite and silver halide containing glasses exhibiting high electronic polarizabilities. The analysis of the conductivity spectra provides strong evidence that the ionic site energy distributions in these glasses are distinct from those in conventional glasses with low electronic polarizabilities, such as silicate, borate, and phosphate glasses. Our results can be explained by postulating a vacancy-type transport mechanism, i.e., by assuming that a high electronic polarizabilty of the glassy network leads to a small and temperature-dependent ratio of empty ionic sites to mobile ions.

Mechanisms of Ion Conduction in Polyelectrolyte Multilayers and Complexes

“…Whereas for mixed alkali glasses the actual shape of the conductivity spectra changes with temperature [54,55], the shape remains constant for the other materials of refs. [52,53]. Instead, in the latter cases the simple proportionality between σ dc T and ν * is not valid anymore.…”

“…Summerfield scaling can be expressed by σ (ν)/σ dc = F (ν/(σ dc T )). This scaling works for many ion-conducting materials, however it fails for systems like single cation glasses with high electronic polarizabilities [52,53] and mixed-alkali borate glasses [54,55]. Whereas for mixed alkali glasses the actual shape of the conductivity spectra changes with temperature [54,55], the shape remains constant for the other materials of refs.…”

Fundamental questions relating to ion conduction in disordered solids

“…There is experimental evidence that in materials with high ion concentration, at any given time only part of the ions are actively involved in back-and-forth motion. 37,38 . A widely applied description of conductivity spectra in the low-frequency regime (i.e., below 100 MHz) is a Jonscher type power law,…”

“…In studies of alkali-germanate glasses and alkali-borate glasses of varying ion content, for instance, subtle changes in the shape of the conductivity spectra were seen to correlate to known anomalies in the glass-transition temperature. 37,38 The glass-transition temperature passes through a maximum as a result of how added modifier ions initially polymerize, but later depolymerize, the oxide network. Consequently, the average oxygen coordination of the ion's charge-compensating sites changes with ion concentration, resulting in modifications of the local ion environment which could mimic changes to the dimensionality of the conduction space.…”

“…Figure 6(b) shows data also for a mixed-alkali glass; these data deviate significantly from the approximate ac universality represented by the red curve. It appears that, on the one hand, the RBM captures the essential features of the ion dynamics for single-ion conducting disordered solids, and that, on the other hand, deviations from the RBM universal ac conductivity may provide important information about specific features of the solid in question 38 . Thus the RBM may be regarded as the "ideal gas" model for ac conduction in disordered solids.…”