Comparing the effects of Ga2O3 and Al2O3 on the structure and mechanical properties of sodium borate glasses

The role of Ga₂O₃ in oxide glasses remains poorly understood compared to other network forming oxides. To address this, we here study the structure and mechanical properties of sodium gallioborate glasses and compare our findings to those of sodium aluminoborate glasses. The substitutions of both Ga₂O₃ for B₂O₃ and Al₂O₃ for B₂O₃ increase the fraction of tetrahedral Ga or Al units and decrease the fraction of tetrahedral B. However, unlike in the case of aluminoborate glasses, higher-coordinated polyhedra (i.e., Ga^V and Ga^VI) are not observed even in the pergallic region. In both glass series, most mechanical properties exhibit a change in their trend at the peralkaline-to-pergallic transition. The substitution of Ga₂O₃ for B₂O₃ decreases the crack initiation resistance, while the substitution of Al₂O₃ for B₂O₃ results in an increase in resistance. In the sodium gallioborate glasses, the fracture toughness increases in the peralkaline region and decreases in the pergallic region.