Tellurite And Fluorotellurite Glasses For Active And Passive

4. Thermal properties and glass stability; MDO 119
workers have studied the structure and thermal properties of binary and ternary WO3-
containing glasses [34-39]. Shaltout et al. [38] studied the thermal properties by DSC and
structure of a series of binary TeO2-WO3 glasses by Raman spectroscopy. Glasses were
formed over a wide compositional range viz.: 5 to 50 mol. % WO3. Tg, Tx and Tx-Tg
increased to a maximum at 27.5 mol. % WO3. Around this composition is where the
maximum population of [WO4] tetrahedra occurred in the glass series. For concentrations
of WO3 > 27.5 mol. %, the W +6 ions were found to exist in an increasing number of six-
fold coordination: [WO6] octahedra. Compositions MOD014 to 016, inclusive, which are
shown in fig. (4.13) contained < 27.5 mol. % WO3, indicating the co-ordination of the
W +6 ions was predominantly tetrahedral [WO4], which resulted in more stable glasses
than for compositions with WO3 > 27.5 mol. %.
Champarnaud-Mesjard et al. [35] studied a wide range of compositions in the ternary
system TeO2-WO3-Bi2O3. Glass formation was found to occur in the TeO2 rich region of
the ternary phase diagram, and this region increased in size as the temperature the glass
was quenched from was increased (650, 700 and 800°C). The most stable composition in
the TeO2-WO3-Bi2O3 series studied here was 70TeO2-25WO3-5Bi2O3 (MOD016) with a
Tx-Tg gap of 152°C [35].
Feng et al. [39] looked at glass formation in the ternary system TeO2-WO3-Nb2O5 and
found the most stable compositions to be 90TeO2-5WO3-5Nb2O5 (equivalent to
MOD014) and 82.5TeO2-7.5WO3-10Nb2O5 (equivalent to MOD015) with Tx-Tg gaps of
173 and 171°C, respectively [39]. Unlike the glasses which contain alkali metal oxides
[28], there is a wide range of ternary compositions of the series TeO2-WO3-MO (where