Oxygen tri-clusters make glass highly crack-resistant

Identifying key structural factors that surmount their intrinsic brittleness and poor crack initiation resistance (C_R) is crucial for designing glass efficiently and predictably. In this study, we present three significant discoveries that contribute to the design of glasses with superior mechanical performances. Firstly, the C_R of the aluminosilicate glasses exhibited a drastic increase when the alumina content surpasses a critical threshold. Secondly, the fraction of three-coordinated oxygens (i.e., oxygen tri-cluster fraction [⁽³⁾O]) was successfully quantified using our new Nuclear Magnetic Resonance technique. Thirdly, a correlation between the evolution trend of the [⁽³⁾O] and the alumina content was established, which aligns closely with the C_R trend. These findings suggest that oxygen tri-clusters play a crucial role in significantly enhancing C_R in aluminosilicate glasses.