Electrochemical impedance spectroscopy study of AgI–Ag2O–MoO3 glasses: understanding the diffusion, relaxation, fragility and power law behaviour

Abstract

ABSTRACT Electrochemical Impedance Spectroscopy and Raman studies are performed on fast ion conducting, AgI–Ag2O–MoO3 glasses, over a wide range of composition to understand the features of structure, ion migration and their correlation. These features essentially involve diffusion and relaxation. The coefficients associated with diffusion process, especially, the diffusion coefficient, diffusion length and relaxation time have been determined by applying Nguyen–Breitkopf method. Besides, by tuning the concentration of the constituents, it is possible to obtain samples those exhibit two important structural characteristics: Fragility and Polymeric phase formation. The present study essentially addresses these issues and endeavours to figure out the corroboration among them. The relaxation behaviour, when scrutinised in the light of Diffusion Controlled Relaxation model, ascertains the fragility threshold which is also identified as the margin between the two types of polymeric phases. Simultaneously, it fathoms into the equivalent circuitry, its elements and their behavioural changes with above mentioned features. The power law behaviour of A.C. conductivity exhibits three different non-Jonscher type dispersive regimes along with a high frequency plateau. The sub-linearity and super-linearity remain significantly below and above the Jonscher’s carrier transport limit, 0.5 ≤ n ≤ 0.9. Finally, by observing the behaviour of the crossover between these sun-linear and super-linear (SLPL) regime, an intuitive suggestion has been proposed for the appearance of SLPL: oxygen vacancy formation at higher frequency.