Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 24
2.3.2.1. TeO2
α-TeO2, or paratellurite, is tetragonal (space group P43212) [2]. Early work suggested the
network in tellurite glasses consisted of strongly deformed [TeO6] units, analogous in
structure to rhombic β-TeO2 (tellurite, space group Pbca), where Te +4 is coordinated to
four oxygens. Fig. (2.2) shows the crystal structure of α- and β-TeO2.
Fig. (2.2): Structure of TeO2: (a) α-TeO2, and (b) β-TeO2 (arrows represent the Te 5s
electron lone-pair) [19].
However, later work proved that in tellurite minerals and glasses, a number of polyhedra
are formed, of Te +4 coordination: 3, 3+1 and 4. In the glasses this variety of coordination
is due to the presence of network modifiers and intermediates [2]. Table (2.2) summarises