Analyzing the Breakdown of the Stokes-Einstein Law in AgI–AgPO3 and M–PO3 (M = Mg, Ca, Sr, Ba) Melts

The Stokes-Einstein (SE) law has been widely used in the analysis of transport properties in the liquid state. However, recent studies have revealed that not all the systems obey this law. Particularly, large deviations from the SE law have been reported for systems that exhibit high ionic conduction in the glassy state. Although this observation has strong implication in the development of electrolyte materials, few fundamental studies on the subject have been done. In a recent study, based on the Bond Strength-Coordination Number Fluctuation model of structural relaxation developed in our group, it was pointed out that the correlated ionic motion starts at a temperature much higher than the glass transition temperature. With the objective to gain a further understanding on that behavior, in the present study we analyzed the temperature dependence of the degree of deviation from the SE law in the melts of AgI–AgPO3 and M–PO3 (M = Mg, Ca, Sr, Ba). The result reveals clearly that the deviation from the SE law increases with the decrease of temperature of the melt, which contrast with the behavior found in other systems. It is also noted that the behavior of the above mentioned two systems differ, and that such difference reflects the degree of ion transport.