Evidence of active regions for ion transport in lithium silicate glasses using the isoconfigurational ensemble

In the context of the ionic transport in glasses, the concept of conduction “channels” (or pathways) has proved to be useful to rationalize both experimental and computational results. While the concept of transport channel is well defined for crystalline solid conductors, in the case of glasses the concept of transport channel is related to an ephemeral region in which mobile ions have found a convenient environment to perform the electrical transport. In this paper we present a way to put into evidence the existence of such regions in the diffusion time scale during a molecular dynamics experiment. To this purpose we use the so-called Isoconfigurational Method (IC) and the associated concept of particle propensity recently introduced by Widmer-Cooper, P. Harrowell, and H. Fynewever (Phys. Rev. Lett. 93, 135701 (2004)). The notion of particle propensity was employed to find the existence of regions which are dynamically more active for the moving particles. We identify these active regions as the most appropriate for a re-arrangement so as to form the conduction “channels” as defined above. These regions are detected from the very beginning and remain the same all along up to and during the diffusion times. Besides, our study reveals that those active regions are surrounded by a high concentration of non-bridging oxygens and consequently they support the scenario proposed by Greaves (J.Non-Cryst. Solids 71, 203 (1985)). ► We present an alternative way to describe “channels” for ionic transport in glasses. ► We use the so-called Isoconfigurational Method and the concept of particle propensity. ► We show the existence of high propensity clusters (HPC) for Li ions in Li2SiO3 glass. ► A HPC consists of a network of sites quickly explored by the diffusing Li ions. ► A HPC has the topological characteristics inherent to the ionic “channels” in glasses.