Silver-ion dynamics close to the superionic phase transition of γ −RbAg4I5 with segregated Ag+

Abstract

The silver-ion dynamics in γ −RbAg4I5 with segregated microcrystals of AgI system was investigated by admittance spectroscopy in its normal phase but close to the superionic phase transition at 120 K. The electrical conductivity relaxation is well described using the conductivity formalism in the frequency domain σ⋆[ω]=σ0{1+(ȷω/ωp)n}(n=1−β) but showing a decrease of the exponent β as the temperature increases toward 120 K, thus indicating stronger correlation between silver ions. The real part of the conductivity follows the dispersive behavior exp[(−t∕τ)β] in a wide range of frequency and the temperature derivative of the dc conductivity, Ea = d(ln[σ0])∕d(1∕T), increases with temperature in the same transition region below 120 K. The observed behavior in conductivity in the normal phase, close to the superionic transition at 120 K when compared with that of pure γ −RbAg4I5, is attributed to an increase of mobile silver-ion defects concentration with increasing temperature due to the presence of the AgI phase. At low temperatures, these defects populate most of the surface of the crystalline grains and they continue to be thermally generated and propagate toward the interior of the grains on increasing temperature, thus increasing ions jumps and correlation among them.