Tellurite And Fluorotellurite Glasses For Active And Passive

9. Conclusions; MDO 376
optical basicity in the glass suppressing movement of Na + and Zn 2+ , particularly
for molar Na2O:ZnO ratio = 1 [4].
• The tungsten-tellurite glasses (90TeO2-5WO3-5Nb2O5, 82.5TeO2-7.5WO3-
10Nb2O5, 70TeO2-25WO3-5Bi2O3 mol. %, with Tg ≈ 350°C) exhibited Tx-Tg >
110°C. Glass stability has been shown to reach a maximum at 27.5 mol. % WO3
where [WO4] tetrahedra content was highest for the binary TeO2-WO3. Above this
mol. % stability decreased and the amount of [WO6] octahedra increased [5].
• Unlike the TZN glasses, the tungsten-tellurite compositions were shown to form
high stability glasses with molar MOx:WO3 ratio = 1, and molar MOx:WO3 ratio ≠
1, i.e. glass formation occurs over a wider range than the TZN glasses.
Fluorotellurite glasses
• Glass formation was shown for the first time in the ternary system TeO2-Na2O-
ZnF2 [6].
• For the series (90-x)TeO2-10Na2O-xZnF2, 5 ≤ x ≤ 30 mol. %, Tg decreased with
ZnF2 content from 273°C (x = 5 mol. %) to 235°C (x = 30 mol. %), due to
depolymerisation of the TeO2 network with fluoride addition [6].
• Glass stability (Tx-Tg) was shown to increase with ZnF2 addition, reaching a
plateau of around 161°C at x = 25 mol. %. This could be due to competition of
various phases to crystallise, and as the eutectic is approached with fluoride
addition [6].