Thermoelectric power of the high ionic conductivity glasses AgI:Ag2O•B2O3

Thermoelectric power determinations allow one to obtain the thermodynamic properties of the ionic species exchangeable at the electrode of the thermocell employed. This may be of some relevance in the case of the high ionic conductivity glasses containing AgI, such as those formed in the pseudobinary AgI:Ag2O·B2O3. The thermoelectric power of the glasses investigated becomes almost T independent in the vicinity of the corresponding Tg. When these T independent values are plotted vs. the composition, expressed as AgI equivalent fraction, the resulting trend is comparable with those observed for binaries of molten salts. The system is treated as a mixture of two kinds of silver ions, i.e., those from AgI and those from silver borate, respectively. By employing the well-known relationship between the thermoelectric power and the entropy of the ionic species exchangeable at the electrode, one may state the suitable ideal behavior of the thermoelectric power vs. the composition and describe the deviations from this as due to the excess entropy of mixing. The trend in the latter is indeed very close to that predicted by the model of regular mixtures. Finally, as the plots of the logarithm of the room temperature conductivity, activation energy, and Tg may be fairly fitted vs. the AgI equivalent fraction by straight lines, it seems likely to suggest that the Ag+ coming from AgI plays a major role in determining the properties of these glasses.