Transparent Glass‐Ceramics With High Hardness and Fracture Toughness

ABSTRACT The development of transparent glass‐ceramics that simultaneously exhibit high fracture toughness, hardness, and optical transparency poses a significant scientific challenge, since enhancement of mechanical properties often compromises visible light transmission via crystallinity‐induced scattering. Here, we report novel MgO‐Al 2 O 3 ‐SiO 2 ‐ZnO‐B 2 O 3 glass‐ceramics that overcome this trade‐off, attaining high indentation fracture toughness ( K IC(ind) = 2.1 MPa·m 1/2 ) and Vickers hardness ( H V = 9.2 GPa) while simultaneously achieving good visible light transmittance (∼74% at 550 nm). The crystallization behavior and residual stress distribution are governed by the interplay between ZnO and B 2 O 3 , where ZnO acts as a network modifier to enhance Mg 2+ mobility and α‐cordierite crystallization, while B 2 O 3 stabilizes the glass matrix through tetrahedral BO 4 linkages, suppressing interfacial stress gradients. Molecular dynamics simulations reveal that thermal expansion mismatch between α‐cordierite and MgAl 2 Si 3 O 10 with the glass matrix generates residual compressive stresses, enhancing crack deflection and interfacial cohesion. A dual‐phase microstructure comprising α‐cordierite (rigid hexagonal framework) and MgAl 2 Si 3 O 10 (energy‐dissipating interfaces) enables mechanical resilience, while controlled crystal size minimizes light scattering. Surface crystallization induces compressive stress (ZC‐6, ‐368.4 MPa) analogous to that produced via ion‐exchange strengthening, effectively counteracting tensile stresses at crack initiation sites. The optimized ZC‐6 composition exemplifies this balance between mechanical and optical performance, surpassing many conventional glass‐ceramics in both fracture toughness and transparency. This work establishes a novel paradigm for designing high‐performance transparent materials, bridging the gap between optical clarity and mechanical resilience.