New oxyfluorotellurite glass: thermal analysis and structural analysis by means of Raman scattering

The TeO2-BaO-BaF2-La2O3-LaF3 oxyfluorotellurite glass system is newly developed. Differential thermal analysis (DTA) and structural analysis by Raman scattering spectra are reported on the 70TeO(2).(20-x)BaO.xBaF(2).(10-y) La2O3.yLaF(3) composition (x = 0, 5, 10, 15, 20; y = 0, 5, 10). The DTA results indicated that an increase of fluoride content in the glasses decreases the glass-transition temperature (T-g) and increases the crystallization-onset temperature (T-c). As a result, the 70TeO(2).20BaF(2).10LaF(3) glass showed a large Hruby's parameter, possessing excellent thermal stability. Changes in glass-network structure with fluoride content are discussed based on the Raman scattering spectra of glasses. The glass-network structures in the 70TeO(2).(20-x)BaO.xBaF(2).(10-y) La2O3.yLaF(3) glasses are basically composed of both Te(O, F)(4) and Te(O, F)(3) units, but the Te(O, F)(4)/Te(O, F)(3) ratio in the glass becomes higher with increasing fluoride content. This may be considered one of the reasons why the 70TeO(2).20BaF(2).10LaF(3) glass exhibits excellent thermal stability. This improved thermal property gives a new possibility of the present oxyfluorotellurite glass for optical applications such as rare-earth-doped fiber fabrication. (C) 2002 Elsevier Science B.V. All rights reserved.