The origin of the nonexponential relaxation of silver ions in the crystalline ion conductor ${\mathrm{Ag}}_7{\mathrm{P}}_3{\mathrm{S}}_{11}$ is analyzed by comparing appropriate two-time and three-time ${}^{109}\mathrm{Ag}$ 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 ${}^{109}\mathrm{Ag}$ 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.

• Received 22 December 2003

DOI:https://doi.org/10.1103/PhysRevB.69.094302