Raman spectra of MO 1/2[sbnd]TeO 2 (M = Li, Na, K, Rb, Cs and Tl) glasses

Abstract

The structure of MO 1/2 TeO 2 (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 TeO 4 trigonal bipyramids (tbp's) and TeO 3 + 1 polyhedra having one non-bridging oxygen atom (NBO). In the glasses containing 20–30 mol% alkali oxide, TeO 3 trigonal pyramids (tp's) having NBOs are formed in the continuous network. When alkali content exceeds 30 mol%, isolated structural units, such as Te 2 O 2− 5 ion, coexist in the continuous network. The fraction of TeO 4 tbp's decreases with increasing alkali content. The glasses, which contain nearly 50 mol% alkali oxide, are composed of a continuous network constituted by TeO 3 + 1 polyhedra and TeO 3 tp's, and of isolated structural units, such as Te 2 O 2− 5 and TeO 2− 3 ions. The structure of thallium tellurite glasses having less than 30 mol% TlO 1/2 is similar to that of alkali tellurite glasses containing equal amounts of MO 1/2 . The fraction of TeO 3 tp's having NBOs in the thallium tellurite glasses, when TlO 1/2 content is equal to or higher than 40 mol%, is larger than that in the corresponding alkali tellurite glasses. In the 66TlO 1/2 ·34TeO 2 glass, most of tellurium atoms are in a form of isolated TeO 2− 3 ion. A new hypothesis is also given for a mechanism for the basic structural changes in the tellurite glasses.