An ionic conduction mechanism for the AgI doped glasses of the system Ag₂O–B₂O₃

In this paper it is proposed that, as long as the glasses of the system Ag₂O–B₂O₃–AgI are demixed on a very fine scale into a silver borate matrix and AgI microdomains, their activation energy for electrical conduction can be considered an average value of the two phases present. These values are taken to be equal to those of silver iodide and of the corresponding undoped silver borate. In this light it is expected that, in the compositional range considered, the following relation holds: E _σ/E _σma=R; where E _σ and E _σma are the activation energies, respectively, of the doped and undoped glass and R is the fraction of Ag⁺ added as Ag₂O. Deviations from this ‘ideal’ behaviour are attributed to the presence, at the boundary of the two phases, of Ag⁺ in mixed neighbour sites, that is, surrounded by negatively charged structural units of both phases. This approach appears to be successful in explaining the compositional dependence of both E _σ and the glass transformation temperature, T _g, of the studied system.