Tellurite And Fluorotellurite Glasses For Active And Passive

9. Conclusions; MDO 377
• These glasses are the most stable ZnF2 containing tellurite compositions reported
to date to the author’s knowledge, with Tx-Tg > 160°C [6].
• Addition of PbF2 (70TeO2-10Na2O-10ZnF2-10PbF2 and 65TeO2-10Na2O-20ZnF2-
5PbF2 mol. %) to the TeO2-Na2O-ZnF2 compositions listed above reduced glass
stability, although Tx-Tg gaps were > 100°C.
• Replacement of Na2O with WO3 in the glass 65TeO2-10Na2O-25ZnF2 mol. %
(65TeO2-10WO3-25 ZnF2 mol. %) resulted in a glass of high stability.
• 65TeO2-10Na2O-xZnF2-(25-x)ZnO, 0 ≤ x ≤ 20 mol. %, glasses showed a different
stability trend to the TeO2-Na2O-ZnF2 glasses: Tx-Tg increased to 168°C for molar
ZnO:ZnF2 ratio = 0.55, then decreased with molar ZnO:ZnF2 ratio > 0.6. Tg
increased with molar ZnO:ZnF2 ratio, with a marked increased at molar ZnO:ZnF2
ratio ≈ 0.6, indicating a structural change in the glass at this point, possibly Zn +2
coordination.
9.2. Crystallisation studies (Chapter 5)
Batch materials
• Batch materials TeO2, ZnO, and Na2CO3 were shown to be phase pure using X-
ray diffraction (XRD).
• However, the as-received ZnF2 was show to contain a significant proportion (see
section 9.4) of Zn(OH)F [7].