Abstract

Raman spectra of xNa 2O−(1− x)TeO 2 glasses were measured and analyzed over a broad composition range. The network structure of the glass consists of a mixture of TeO 4 trigonal bipyramids and TeO 3 trigonal pyramidal units. Increase of alkali content results in conversion of the TeO 4 units into TeO 3 units with a varying number of non-bridging oxygen atoms. This local structure transformation becomes more evident at x=0.2, where rigidity percolation theory predicts a threshold for the rigid-to-floppy transition. However, other spectral features such as the composition dependence of the energy of the Boson peak do not support the occurrence of the stiffness transition. The controversial dependence of dynamical parameters such as the fragility index as a function of Na 2O concentration is also discussed.

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