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

Solid-state 87Rb NMR has been used to determine the ionic hopping rate of Ag+ ions in a powdered sample of α-RbAg4I5 as a function of temperature from 20 to 250 °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 87Rb has a large quadrupole moment, making 87Rb NMR capable of detecting mobile species in close proximity. Simulation of the static 87Rb 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 °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.