Structural origin of the mixed alkaline earth effect in alkali‐free aluminosilicate glasses revealed by AIMD simulations

Abstract The mixed alkaline earth effect, a unique phenomenon in glass science that induces non‐linear variations in glass properties, has not been clearly established its structural origin. Especially, when there are more than two alkaline earth oxides (RO) in the system, the mechanism becomes more complex. In this work, we attempt to explore the structural origin of the mixed alkaline earth effect in alkali‐free aluminosilicate glasses by combining experiments with ab initio molecular dynamics simulations (AIMD). The experimental results show that the glass transition temperature, softening temperature and reheating shrinkage change nonlinearly with different MgO/CaO ratios. Subsequently, the AIMD simulations are employed to reproduce the glass network structure and observe the mixed alkaline earth effect successfully, which compensated for the limitations of classical molecular dynamics (CMD) simulations. It is found that the non‐linear changes in the experiments are related to the mid‐range structure of the glass. And the simulation further confirmed the influence of Mg 2+ on the formation of small‐sized rings and [AlO 5 ] in glass. More importantly, the short‐range structure of the glass, such as bond length, coordination number and bond angle distributions, also vary nonlinearly with different MgO/CaO ratios. We confirm that the mixed alkaline earth effect is a universal existence in the glass structure. It is not only related to the mid‐range structure, but also reflected in the short‐range structure of the glass.