Glass Formation Area and Structural Analysis of the Rich TeO₂ Zone in the CdO-TeO₂-GeO₂ System

This study systematically explored the glass formation region of the ternary CdO-TeO₂-GeO₂ glass system using the conventional melt-quenching method. Thirty-six compositions with varying TeO₂ contents and relative CdO proportions were synthesized at melting temperatures of 900 °C-1200 °C, revealing a broad glass formation region that included fully transparent and partially crystallized glasses. The structural and thermal properties of representative TeO₂-rich compositions were investigated. X-ray diffraction analysis confirmed predominantly amorphous structures across most of the investigated compositional range, while weak diffraction peaks were observed in compositions with the highest CdO contents, indicating the onset of crystallization; besides, the S26 sample showed three characteristic peaks corresponding to Cd₃TeO₆. Energy-dispersive X-ray spectroscopy confirmed Cd, Te, and Ge as the main glass constituents. Observed deviations from nominal compositions were attributed to Te volatilization, elemental redistribution during melting, and partial Al incorporation from the alumina crucible. Raman and Fourier-transform infrared spectroscopic results revealed the progressive depolymerization of the tellurite network with increasing CdO content, which was associated with the transformation of TeO₄ units into TeO₃₊₁ polyhedra and TeO₃, together with changes in the coordination environment of Ge ions, suggesting the coexistence of GeO₄ and GeO₆ units. Differential scanning calorimetry revealed glass transition temperatures of 416 °C-495 °C. CdO-rich compositions exhibited multiple crystallization events, whereas TeO₂-rich compositions remained amorphous up to 800 °C, indicating that CdO promotes devitrification, whereas GeO₂ enhances thermal stability.