A comprehensive treatment of universal dispersive frequency responses in solid electrolytes by immittance spectroscopy: low temperature AgI case

Abstract

Motivated by the recent work on β″-alumina polycrystalline ceramics, we revisit the frequency dispersion behavior of AgI. Series of admittance and capacitance Bode plots at different temperatures revealed the presence of well-defined parallel capacitance effects and power-law frequency dependencies. Non-trivial bulk dispersion is thus successfully described by the bulk conductance with activation energy of 0.262 eV in parallel connection to several capacitive effects: (i) a mobile-charge contribution, universally observed in many solid electrolytes, approximated by a Cole-Davidson model with Δ𝜖 C ≅ 28, γ C ≅ 0.388, and (τ C)−1 thermally activated by 0.237 eV, (ii) a dipolar and vibratory contribution represented by another Cole-Davidson model of the dielectric strength of Δ𝜖 D ≅ 9.0 with γ D ≅ 0.110, τ D ≅ 0.003 s, corresponding to Nearly-Constant-Loss behavior, and (iii) high frequency limit capacitance corresponding to the dielectric constant 𝜖 S ≅ 6.4. Electrode effects are described by an ideal Warburg response and the coefficient activated by 0.165 eV, which is connected in parallel to the bulk capacitive elements (i) to (iii). The modeling allows a simulation of ac behavior of AgI as a function of temperature as well as frequencies, addressing all of the universally observed dispersive responses.