Dynamics of Ag+ Ions in RbAg4I5 Probed Indirectly via Rb-87 Solid-State NMR

Solid-state Rb-87 NMR has been used to determine the ionic hopping rate of Ag+ ions in a powdered sample of alpha-RbAg4I5 as a function of temperature from 20 to 250 degrees C. In this phase, Rb is a stationary framework atom, which does not take part in ionic conduction in this material. At the same time Rb-87 has a large quadrupole moment, making Rb-87 NMR capable of detecting mobile species in close proximity. Simulation of the static Rb-87 NMR powder pattern under the influence of Ag+ motion was performed using the EXPRESS software. Lineshape simulations were used to extract an ionic hopping rate for each temperature, and changes in the line shape were correlated to changes in ion mobility, which increases with temperature. Ag+ hopping rates were found to be in the range of 7.0 +/- 0.5 kHz to 30 +/- 2 kHz within the temperature window of 20 to 100 degrees C, resulting in an activation energy of 17 +/- 3 kJ/mol (0.18 +/- 0.03 eV), for silver ion hopping. This result is in agreement with previous studies, suggesting that this indirect method of detecting ion mobility can be extended to other ion conducting materials.