Origin of nonexponential relaxation in a crystalline ionic conductor:: A multidimensional 109Ag NMR study -: art. no. 094302

The origin of the nonexponential relaxation of silver ions in the crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate two-time and three-time Ag-109 NMR correlation functions. The nonexponentiality is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an intrinsic nonexponentiality. Thus, the data give no evidence for the relevance of correlated back-and-forth jumps on the time scale of the silver relaxation. Further, four-time Ag-109 NMR correlation functions indicate exchange processes between fast and slow silver ions that take place on the time scale of the silver jumps and, hence, the dynamical heterogeneities are short lived.