Distribution of tellurite polymorphs in the xM2O-(1-x)TeO2 (M = Li, Na, K, Cs, and Rb) binary glasses using Raman spectroscopy

Raman spectra of xM(2)O-(1 - x)TeO2 (M = alkali metal atom) binary glass-forming oxide systems were measured over a wide composition range and for all alkali-types in an effort to extend the structural aspects of previous works on this field and reveal the composition- and modifier type-induced structural changes in a quantitative manner for the first time. Analysis of the Raman spectroscopic data after a reduction procedure and focusing on spectral effects caused by structural changes allowed the quantitative monitoring of the well-known transformation of the TeO4 (predominating in the low modifier content glass) into TeO3 trigonal pyramids at increased alkali content. The main finding pertains to the estimation of the relative populations of the basic building blocks for a wide compositional range and for different alkali-types directly from the Raman spectroscopic data, thereby permitting the calculation of the average number around Te atoms versus modifier content and alkali-type. The variation of the coordination number implies that the structure of all M2O-TeO2 tellurite glasses with the same composition is comparable and almost independent of alkali-type. Spectroscopic evidence suggests that the presence of neutral trigonal pyramid TeO2/2(=O) units is questionable, while the increase of M2O content leads to a gradual transformation of TeO4/2 initially to TeO3/2O- and then to TeO1/2O-(=O) trigonal pyramid units depending on the modifier content. The structural model based on Raman spectroscopic results is in agreement with the findings of NMR work on binary alkali-tellurite glasses. (C) 2011 Elsevier B.V. All rights reserved.