On the lifetime of dynamical heterogeneities associated with the ionic jump motion in glasses: Results from molecular dynamics simulations and NMR experiments

Recording four-time correlation functions in experiments and computer simulations, we measure the lifetime of dynamical heterogeneities associated with the ionic jump motion in phosphate glasses. Ag-109 NMR four-time correlation functions for a silver iodide doped silver phosphate glass indicate that the silver ions exhibit a random new rate from a broad distribution after very few jumps, implying that silver sites featuring fast and slow ionic jumps are intimately mixed rather than grouped into extended domains. Likewise, four-time correlation functions from molecular dynamics simulations of LiPO3 glass show that the dynamical heterogeneities observed for the lithium ionic jumps are short lived. Hence, rapid rate exchange is an important feature of the ion dynamics in an experimental and a model phosphate glass, i.e., the ionic diffusion is comprised of a random series of fast and slow jumps. In addition, we perform simulations for various lattice models to elucidate the interpretation of NMR four-time correlation functions for solid ion conductors, which can differ from that in previous applications of this method. (c) 2006 Elsevier B.V. All rights reserved.