RESUMEN
High-resolution X-ray pair distribution functions for molten and glassy TeO2 reveal coordination numbers nTeO ≈ 4. However, distinct from the known α-, ß-, and γ-TeO2 polymorphs, there is considerable short-range disorder such that no clear cutoff distance between bonded and nonbonded interactions exists. We suggest that this is similar to disorder in δ-TeO2 and arises from a broad distribution of asymmetric Te-O-Te bridges, something that we observe becomes increasingly asymmetric with increasing liquid temperature. Such behavior is qualitatively consistent with existing interpretations of Raman scattering spectra, and equivalent to temperature-induced coordination number reduction, for sufficiently large cutoff radii. Therefore, TeO2 contains a distribution of local environments that are, furthermore, temperature dependent, making it distinct from the canonical single-oxide glass formers. Our results are in good agreement with high-level ab initio cluster calculations.
RESUMEN
The structure and spectroscopic properties of B 2O 3 glass are examined from a theoretical point of view by using a model of 20 B 2O 3 molecules at the DFT/6-31G* level of theory and no predetermined constraints. Useful results are deduced regarding the structure, the fraction of boroxol rings, and the infrared and Raman spectra.