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

•We study the structure and mechanical properties of sodium gallioborate glasses•We compare the effect of adding Ga2O3 to that of adding Al2O3•Both additions decrease the fraction of tetrahedral B units•Ga2O3 for B2O3 exchange increases crack resistance, while it is opposite for Al2O3 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., GaV and GaVI) 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 increases the crack initiation resistance, while the substitution of Al2O3 for B2O3 results in a decrease in resistance. In the sodium gallioborate glasses, the fracture toughness increases in the peralkaline region and decreases in the pergallic region.