Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 230
molecular water in alkali-silicate glasses, evidenced by the characteristic absorption band
at 1600 cm -1 (fundamental H-O-H bending mode) and a broader band around 3600 cm -1
which occurred for the water vapour treated glasses. Two equilibria must be taken into
account when considering hydrolysis of a glass melt [20] (where R is the main glass
forming cation e.g. Si 4+ or Te 4+ ):
(i) Water vapour entering the melt as molecular water (i.e. [H2O]vapour ↔
[H2O]melt).
(ii) Molecular water in the melt hydrolysing the molten network (i.e. [R-O-R]melt
+ [H2O]melt ↔ 2[R-OH]melt).
Therefore the coexistence of these two equilibria in the melt seems to suggest the
probable non-zero concentration of molecular water in any glass with a non-zero water
content [20].
Scholze [17] identified a band around 2800 cm -1 for alkali metal silicate glasses and
attributed this to the stretching mode of the Si-OH group that forms the weaker hydrogen
bonding with the non-bridging oxygens (NBO’s) of the Q 2 or Q 3 tetrahedron (where Q n is
a SiO4 tetrahedron with n bridging oxygen bonds to the surrounding network). Ryskin
[22, 23] also identified a stretching mode of the hydrogen-bonded Si-OH groups around
2800 cm -1 in crystalline hydrated silicates. It is proposed in the current study that the
band, which occurs around 3060 cm -1 for tellurite and fluorotellurite glasses (fig. (6.17))
be attributed to the stretching mode of the weakly hydrogen-bonded Te-OH groups [5].