Revealing the effect of medium-range structure on silicate glass hardness

Atomic structure determines physical properties, but for glassy materials, the nature of structure-property relationships remains ambiguous. Since glass properties are governed by both chemistry and structure, it is difficult to dissociate these two effects. Here, the sole effect of the structure on property is isolated by treating an industrial aluminosilicate glass with either thermal-annealing or pressure-quenching processes to produce glasses with varying densities and hardnesses (at constant composition). To explore the underlying structural origin of property changes, neutron total-scattering patterns of these glasses were measured. These results confirm the applicability of rigid-unit mode theory since the short-range tetrahedra were found to remain unaffected. In contrast, close correlations are derived between properties and medium-range structure (as encoded in various features of the first sharp diffraction peak). Overall, it reveals that the increase in the medium-range order is the structural origin of the extra extent of hardness increase beyond the densification effects.