LAUSR

The xAgI–(1 – x)AgPO3 glass system exhibits a wide and well-known range of variation in silver ion conductivity with the AgI molar ratio, x, while the total concentration of Ag+ ions does not change significantly. We propose an interpretation to explain this effect, based on the fact that only a fraction of Ag+ cations are effective charge carriers and that their concentration is determined by a dissociation equilibrium of AgI in the AgPO3 glass. In this case, the ionic conductivity stems from the thermodynamic activity of silver iodide, aAgI, dissolved in the AgPO3 glass. To verify this relationship experimentally, aAgI is determined from electromotive force measurements of solid-state cells in the temperature range of 25–90 °C. Our results reveal a linear dependence of silver ion conductivity on aAgI over 3 orders of magnitude. The substantial variations in aAgI observed with the increase in the AgI molar ratio x are justified assuming a regular solution model for the AgI–AgPO3 mixture.