Effect of grain boundaries on the low-temperature ionic conductivity of polycrystalline RbAg4I5 and Ag3SBr

Abstract The influence of grain boundaries on dc and ac conductivities of polycrystalline RbAg 4 I 5 and Ag 3 SBr was studied in the temperature range 15 K T T t T T t the ion transport occurs preferentially along paths at the grain boundaries with very low activation energy, whereas the conventional conduction through the grains and across grain boundaries dominates at T ∗> T t . A long-time relaxation effect is observed around the transition temperature ( T ≈ T t ). This effect is attributed to a subsurface superionic transition leading to a formation of a subsurface superionic phase at the grain boundaries. The analysis of experimental results shows that the temperature-independent high-frequency ac conductivity observed at T + ions in preferred sites with an appropriate distribution of relaxation times.