A study was made of the far-infrared spectra of glasses of the form, (1-x)GeO2-xRb2O, where x was between 0 and 0.27. The results showed that, when x was less than 0.075, the Rb ions occupied one type of site. At higher Rb contents, 2 types of site were occupied. The frequencies of ionic motion were such that the value for the site which was occupied at low Rb contents was between the values for the 2 sites which were occupied at higher Rb contents. The motion with the highest frequency was associated with sites that were similar to those in the crystal. The motion with the lowest frequency was associated with so-called secondary sites which had no equivalent in the crystal. It was noted that, according to the free-ion model, ionic conductivity should be due mainly to Rb ions in sites with the intermediate and highest motion frequencies. However, such a model could not predict the compositional dependence of the activation energy for conduction correctly because it did not take proper account of strains in the glass network.

E.I.Kamitsos, Y.D.Yiannopoulos, H.Jain, W.C.Huang: Journal of Non-Crystalline Solids, 1996, 203, 312-9