Revealing structural role of ZrO2 in silicate glasses from macroscale property by rigid-unit packing fraction method

The structural role of an oxide as a former and modifier can have significant effects on the chemical durability and mechanical properties of the glass. Some oxides with high-field strength cations, for example, MgO and ZrO2, are often labeled as a third group-intermediate, due to their either undetermined or dual structural roles dependent on the glass compositions. Based on our recent modification of the Makishima-Mackenzie (MM) model using the rigid-unit Packing Fraction (RUPF), we analyzed a series of novel zirconia-containing bioactive glasses. The RUPF-based MM-model provides better prediction of the elastic moduli of these new glasses in comparison to experimental measurements. At the same time, the structural role of zirconia can be determined by comparison with calculations by assuming various structural roles and those from experiments. We reveal that ZrO2 acts as the network former in phosphosilicate glasses, which leading to significant increase in packing fraction and consequent increase in Young's modulus. The recent experimental and atomistic simulation results support the glass former role of zirconia in silicate glasses. This method is general and applicable to other oxides in glasses.