Structure and ionic conduction in the Ag2O·WO3·TeO2 glass system

Preparation, characterization by X-ray diffraction, differential scanning calorimetry, X-ray photoelectron spectroscopy (XPS), Raman and Fourier transform–infrared (FT–IR) spectroscopy and electrical conductivity studies have been carried out on the yAg2O · (1−y) [xWO3·(1–x) TeO2] glass system. The compositional variation of the glass transition temperature and the calculated oxygen packing density values have been correlated. The conductivity at ambient temperature shows two maxima for the compositions corresponding to y = 0.30 and 0.40 at x = 0.2 and 0.4, respectively. The observed conductivity enhancement is about an order of magnitude and it is correlated to the structural modifications due to the WO3 incorporation into the TeO2 glass network. From the XPS spectra, the binding energies (BEs) of the Ag 3d, Te 3d, W 4f and O 1s core-levels have been determined. The O 1s spectrum is found to consist of two peaks due to the presence of Te–eqOax–Te, W–O–W, W–O, Te = O, Te–O−1 and W–O−1 oxygen species. The tungsten ions appear to exist in 5+ and 6+ oxidation states in these glasses. The proportion of the reduced tungsten ion is found to decrease with an increase in the WO3 concentration, while that of the Te–eqOax–Te species decreases as x increases. The FT–IR and Raman spectra of these samples reveal that the glass network consists of TeO4, TeO3, WO4 and WO6 polyhedra.