RAMAN-SPECTRA OF MO(1/2)-TEO2 (M = LI, NA, K, RB, CS AND TL) GLASSES

The structure of MO1/2-TeO2 (M = Li, Na, K, Rb, Cs and Tl) binary glasses has been studied by means of Raman spectroscopy. The glasses having low alkali content have a continuous network constructed by sharing corners of TeO4 trigonal bipyramids (tbp's) and TeO3+1 polyhedra having one non-bridging oxygen atom (NBO). In the glasses containing 20-30 mol% alkali oxide, TeO3 trigonal pyramids (tp's) having NBOs are formed in the continuous network. When alkali content exceeds 30 mol%, isolated structural units, such as Te2O52- ion, coexist in the continuous network. The fraction of TeO4 tbp's decreases with increasing alkali content. The glasses, which contain nearly 50 mol% alkali oxide, are composed of a continuous network constituted by TeO3+1 Polyhedra and TeO3 tp's, and of isolated structural units, such as Te2O52-and TeO32- ions. The structure of thallium tellurite glasses having less than 30 mol% TlO1/2 is similar to that of alkali tellurite glasses containing equal amounts of MO1/2. The fraction of TeO3 tp's having NBOs in the thallium tellurite glasses, when TlO1/2 content is equal to or higher than 40 mol%, is larger than that in the corresponding alkali tellurite glasses. In the 66TlO1/2.34TeO2 glass, most of tellurium atoms are in a form of isolated TeO32- ion. A new hypothesis is also given for a mechanism for the basic structural changes in the tellurite glasses.