Influence of quenching rate and quenching media on formation of TeO₂ glasses

In present investigation, the formation of tellurite (TeO₂) glass system was studied without using any external network former & modifier and systematically analyzed by varying the quenching-cooling media. Five samples using TeO₂ melt were prepared employing the different quenching media such as mold at 200 °C, at room temperature, at ice slab, in ice water, and direct in ice slab abbreviated as G1, G2, G3, G4, and G5, respectively. Structural, thermal, optical and electrical properties were studied in order to understand their physical behavior. These samples were found dense enough which manifest the compactness and network rigidity of the structure. X-ray diffractograms confirmed the pure glass (amorphous) phase for sample G5, whereas an amorphous structure with some crystalline phases was observed for other samples. Elemental confinement and oxidation state of tellurium was verified by XPS analysis of the samples. An increase in crystallization temperature (T_c) and considerable shifting in the glass transition temperature (T_g) were observed with the increase in quenching temperature. Optical studies suggested the presence of both direct and indirect allowed transitions in the synthesized samples. All samples were also found to possess high refractive index values (> 2). FTIR and Raman studies confirmed the bonding of the glass and semicrystalline-glass samples and corroborated with the experimental findings. The factors responsible for the formation of glass and crystalline glasses of TeO₂ were pointed out and discussed in detail. A correlation between the structural changes and the physical characteristics of all TeO₂ glass and crystalline-glass samples has been established.