Ionic conductivity and glass transition in superionic conducting glasses (Agi)_{1 - x}(Ag₂MoO₄)_x (x = 0.25, 0.3, 0.35). II. Structural relaxation and excess-free-volume theory

A theory of the structural relaxation and its effect on the ionic conductivity in superionic conducting glasses is presented by extending the excess-free-volume theory for normal glasses. The dependence of the ionic conductivity on time, temperature and cooling-heating rate is discussed for the Agl-Ag₂MoO₄ system which forms superionic conducting glasses. The present approach is applicable to a quantitative interpretation of the bifurcation of the observed conductivity from the Vogel-Tumman-Fulcher (VTF) law to the Arrhenius type at the glass transition temperature as well as other anomalous behaviours observed in the glass transition region (deviations from the Arrhenius law, annealing and hysteresis effects, etc.). The numerical results indicate that the activation volume of a silver cation should be much smaller than the average volume per ion; this appears to be of central importance in accounting for the superionic conducting process in such silver-ion-containing glasses.