Crystallization of TeO2-Nb2O5 glasses and their network structural evolution

TeO2-Nb2O5 glass is a kind of heavy metal oxide glass with a chain-like network structure, in which Nb5+ ions connect the Te-O chains and adjust the types of [TeOx] (x = 3, 4) coordination polyhedra to stabilize the glass network. (100 - y)TeO2-yNb2O5 (y = 3-20 mol %) glasses were prepared, the crystallization behaviour and their network structural evolution were studied by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR). The results show that the stabilization of the TeO2-Nb2O5 glass network is greatly influenced by the constitution of Te-O chains and their linkage. The glass structure with lower Nb5+ content is inhomogeneous, it is composed of edge sharing Te-O chains, partly edge sharing chains connected by Nb5+ ions, apical sharing chains and apical sharing chains connected by Nb5+ ions. Crystalline phases of ß-TeO2, Nb2Te4O13, .beta.-TeO2 and Te3Nb2O11 will be formed in turn when the treatment temperature of the glass is increased. When the concentration of Nb5+ ions is sufficient to well connect Te-O chains, the glass network will tend to homogenize, only one crystalline phase, Nb2Te4O13, will be formed. A suitable preheat treatment will also help to homogenize the glass structure and make the glass more stable.