Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO2-xBi2O3-(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi2O3 content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi2O3 content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi0.864Te0.136O1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.