Structural and Physical Properties of TeO2-B2O3-ZnO Glasses: Evidence of the Mixed-Glass-Former Effect

Abstract

The mixed-glass-former effect (MGFE) remains one of the most intriguing yet least understood phenomena in glass science, particularly for tellurite-borate systems modified by ZnO. This study aims to unravel the structural and physical origins of the MGFE by investigating a series of (100 – x) (70TeO₂ – 30B₂O₃) – (x)ZnO (x = 0, 5, 10, 15, 20 mol%) glasses synthesized via the conventional melt-quenching technique. X-ray diffraction confirmed fully amorphous structures for all samples. FTIR spectra revealed progressive transformation of Te-O-Te linkages into Te-O-B and Zn-O-Te bonds as low frequency band near 930 cm^-1 shift towards higher wavenumber as increasing ZnO mol%, signifying compositional rearrangement within the glass network. The density, molar volume, and oxygen packing density exhibited non-linear variations at 15 mol% of ZnO content, providing experimental evidence of the MGFE. SEM-EDX analyses verified homogeneous microstructure and uniform elemental distribution, confirming that ZnO was successfully incorporated without phase segregation. These findings demonstrate how ZnO acts as both an intermediate oxide and a network modifier, simultaneously strengthening and depolymerizing the glass framework. The comprehensive correlation between structural and physical parameters provides new insights into the fundamental nature of the MGFE and offers a compositional pathway for designing high-density, optically stable tellurite-borate glasses for photonic applications.