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-sigma/E-sigma ma = R; where E-sigma and E-sigma ma 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-sigma and the glass transformation temperature, T-g, of the studied system.