Silver ion dynamics in silver borate glasses:: spectra and multiple-time correlation functions from 109Ag-NMR

The motion of silver ions in (AgI)(x)-(Ag2O-B2O3)(1-x) glasses with AgI concentrations of x = 0.5 and 0.7 was studied using Ag-109-NMR The NMR spectra were analyzed in terms of a superposition of two different contributions. These are associated with Ag ions, which hop on vastly different time scales. The existence of dynamic heterogeneity, i.e. the existence of slow and of fast contributions to the hopping dynamics was directly demonstrated using a four-time stimulated-echo experiment. The results are compatible with an intrinsically exponential response. From measurements of the spectra and of two-time correlation functions a Gaussian distribution of energy barriers, hindering the ionic motion, could be mapped out. (C) 2004 Elsevier Inc. All rights reserved.