Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 23
Thermal expansion coefficients for these systems were 20 to 40×10 -6 °C -1 over the 100
to 200°C region, and refractive indices > 2.1 for TeO2-PbO and TeO2-PbO-SeO2 glasses
(at 578 nm) [14]. All glasses were found to be durable to the laboratory atmosphere.
Glasses which contained BaO, Na2O, Li2O, and B2O3 were least durable when exposed to
an atmosphere saturated with water vapour at around 50 to 55°C. All glasses were
slightly attacked by citric acid, and sodium carbonate solution. However, heavy attack of
the alkali was shown by the binary TeO2-PbO glasses, and the ternary lead tellurite
glasses containing P2O5, ZnF2, BaO, Li2O and Na2O, as well as the TeO2-BaO-As2O5
glass. Glasses containing d-block oxides: MoO3, WO3 and Nb2O5 showed the best overall
resistance to acid, alkali and water [14].
The next early study of note, by Redman et al. in 1967 [18], was on zinc tellurite
glasses. These glasses had a Knoop hardness of around 270, much lower than silica
(540). The transmission of these glasses was from around 380 nm to 6.6 µm, with OH
absorption bands at 3.35 and 4.5 µm. Increasing TeO2 content shifted the electronic
absorption edge to longer wavelengths, and good rare-earth solubility was shown (1 mol.
% Nd2O3), showing promise for a host glass for stimulated emission. Optical surfaces
showed resistance to attack of cold water, with slight attack from boiling water and dilute
acid, and strong attack from concentrated acids and dilute alkali [18].
2.3.2. Structure
In this section the structure of the four main constituents in the glasses studied here will
be summarised: TeO2, ZnO, Na2O, and ZnF2.