Fractal Nanochannels as the Basis of the Ionic Transport in AgI-Based Glasses

Abstract

We propose a new model to explain the transport properties of AgI-based fast ion conducting glasses. The main factor affecting the ionic conductivity is the mobility of the Ag+ carriers, that is controlled by the Ag local environment. We model the ionic conductivity in terms of a percolation between a low-conducting phase (purely oxygen-coordinated sites), and a high-conducting one (iodine/oxygen, I/O, coordinated sites). The percolation takes place along pathways with fractal structure. The nature of the glass network, and namely its connectivity and dimensionality, plays a significant role only for low I/O values, originating the transport and thermal anomalies observed in borate and phosphate glasses.

Solid-State Lithium Ion Electrolytes

“…Figure 9 reports the room temperature conductivity for several compositions as a function of LiI content. It seems that conductivity tends to a limiting value of approximately 10 −3 Ω −1 cm −1 as also reported for silver glasses doped with AgI [57].…”

“…This model was recently proposed by Mustarelli et al [57] in order to describe the transport properties of AgI-based glasses. It is based on previous Reverse Monte Carlo (RMC) structural models of borate and molybdate glasses [58], coupled with bond valence calculations, which showed that the conductivity is related to the formation of "infinite pathways clusters" for transport, where the silver ions do experience a mixed iodine/oxygen (I/O) coordination.…”

Fundamental questions relating to ion conduction in disordered solids

“…Thus while it is a potentially useful idea, more theoretical work is needed before observations of electrode effects may lead to safe conclusions regarding the number of mobile ions (see the next section that outlines the a simple approximate description); one still needs to specify the time scale that the number of mobile ions refers to. -Solid-state NMR methods such as motional narrowing experiments 46,47,48 and the analysis of multi-time correlation functions of the Larmor frequency, 49,50 provide information about the number of ions moving on the time scale that these methods monitor (milliseconds to seconds).…”

A microscopic interpretation of the bulk anomalies in AgI–Ag2O · 2B2O3glasses

“…In our previous paper [8] we demonstrated that the behaviour of the ionic conductivity in AgI-based glasses is chiefly determined by the Ag + local environment, and namely by the iodine-to-oxygen (I/O) ratio in its first coordination sphere. In this frame, purely O-coordinated sites will constitute a sort of "low-conducting phase", whereas mixed I/O sites will belong to a "high-conducting" one.…”

“…We have recently proposed a new model to explain the transport properties of AgI-based fast ion conducting glasses [8]. In our model the main factor affecting the ionic conductivity is the mobility of the Ag + carriers, that is substantially controlled by the Ag local environment.…”