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

✍ Scribed by G. Staikov; M. Nold; W.J. Lorenz; A. Froese; R. Speck; W. Wiesbeck; M.W. Breiter

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 754 KB
• Volume: 93
• Category: Article
• ISSN: 0167-2738
• DOI: 10.1016/s0167-2738(96)00496-1

✦ Synopsis

The influence of grain boundaries on dc and ac conductivities of polycrystalline RbAg,I, and Ag,SBr was studied in the temperature range 15 K < T < 298 K using low-frequency EIS and high-frequency waveguide measurements. A change of the ion conduction mechanism is found at a transition temperature in the range 60 K < T, < 90 K. The conductivity behaviour shows that at 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,.

A long-time relaxation effect is observed around the transition temperature (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 < 100 K can be explained by a model involving a Debye relaxation of Ag + ions in preferred sites with an appropriate distribution of relaxation times.