Fracture behavior of barium titanosilicate glass-ceramics: Role of titanium bond switching and stress fields

Fracture toughness of oxide glasses can be improved through controlled crystallization, resulting in so-called glass-ceramics. However, to fully exploit their potential, a deep understanding of the fracture mechanism is needed. In this work, we investigate the structural origin of the variation in fracture toughness of barium titanosilicate glass-ceramics with varying crystallinity by combining experiments and molecular dynamics simulations. Generally, the glass-ceramics exhibit improved hardness, elastic modulus and fracture toughness compared to the precursor glasses. The simulation results of 40BaO-20TiO2-40SiO2 glass-ceramics revealed that the differences can be attributed to a large extent of titanium bond switching events, namely, the change of the titanium coordination number under stress to dissipate mechanical energy. We also show that by tuning the content and aspect ratio of the formed fresnoite crystals, the fracture behavior of the glass-ceramics can be modified due to the redistribution of the stress field before fracture, which in turn controls the fracture path.