Effect of Early‐Stage Crystallization on the Mechanical Properties of Transparent Niobium Silicate Glass Ceramics

ABSTRACT Although various strengthening strategies are being exploited to address the inherent brittleness of glasses, they often fail in integrating fracture resistance with preserved transparency, making the pursuit of robust yet transparent glass‐based materials a compelling challenge. In this work, we report heat treatment‐induced increases in hardness and elastic stiffness in the Rb 2 O–Nb 2 O 5 –SiO 2 glass‐ceramic system, associated with prominent nanocrystallization but minimal optical scattering. The observations may be rationalized on the basis of a relaxation‐assisted crystallization scenario, in which short‐range ordering near T g may facilitate extensive nucleation, whereas subsequent crystal growth appears to be limited by diffusion barriers and steric hindrance. In the considered system, the approach results in a microstructure with crystallite sizes in the range of 10 nm. This is accompanied by increased hardness and elastic moduli without compromising on optical scattering, even before crystals are observed by X‐ray diffraction, providing an avenue for further extension to other glass chemistries.