Structural Role and Mechanical Impact of Zirconia in Lithium Disilicate Glass

The intrinsic brittleness of oxide glasses limits their use in mechanically demanding applications. In this article, we integrate topological constraint theory (TCT), molecular dynamics (MD) simulations, and experimental characterization to elucidate how ZrO 2 alters the structure, topology, and mechanical response of lithium disilicate (LS2) glass. Glasses with varying compositions of x ZrO 2 –(100 − x )Li 2 Si 2 O 5 ( x = 0–5 mol%) were synthesized and characterized by inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES), x‐ray diffraction (XRD), and 29 Si magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy. MD revealed that Zr 4+ incorporates as a network former, forming Si–O–Zr bridges and ZrO 6 octahedra, which increase the number of topological constraints (), enhance packing density, and reinforce the Si–O–Zr backbone. Increasing the ZrO 2 content monotonically raised density (2.32 → 2.51 g/cm 3 ), Young's modulus (76 → 94 GPa), and hardness (4.9 → 5.9 GPa). However, the crack resistance (CR) reached its maximum of ∼6.0 N at 1 mol% ZrO 2 (where ≈ 3), increasing from ∼4.5 N in the undoped LS2 glass and declining thereafter. This decline could be attributed to Li + clustering and growth of edge‐sharing Li–Si/Li–Zr polyhedra observed in MD simulations, which could localize stress within Li‐rich regions once the network becomes over‐constrained (> 3). These findings suggest that optimal CR arises in the isostatic region, where a balance between rigidity and stress accommodation is maintained.