Tellurite And Fluorotellurite Glasses For Active And Passive

8. Fibre drawing; MDO 359
β-relaxation which occurs mainly below Tg, possibly due to non-cooperative atom
movements. The Vicker’s hardness of fragile glasses such as TeO2- and Bi2O3-based
systems, was shown to decrease rapidly at around T/Tg = 0.9 to 1.0 (i.e. just below Tg).
For stronger glass formers based on P2O5 and SiO2, this behaviour was observed at T/Tg =
1.0 to 1.1 (i.e. just above Tg). This is thought to be due to β-relaxation processes playing a
grater role in the rheological properties of fragile glasses, whereas α-relaxation is more
prominent in the stronger glasses [24].
The slope at any point of fig. (8.16) is equal to the activation energy for viscous flow
[25]. Fig. (8.17) shows the differential curve of the fragility plot of glass MOF001 (25
mol. % ZnF2).
d[log 10 (ηη)] / d(T g /T) / Pa.s
22
20
18
16
14
12
10
8
6
4
0.0 0.2 0.4 0.6 0.8 1.0
T g /T
Fig. (8.17): Differential of fragility plot for glass MOF001 (25 mol. % ZnF2).