Atomic‐scale insight into Li ⁺ /Pb ²⁺ synergy for optimized properties in fluorozirconate fiber glasses

Abstract Fluorozirconate glass optical fibers are important for applications in mid‐infrared spectroscopy, clinical medicine, and industrial processing. Achieving synergistic control of the refractive index and robust anti‐crystallization performance in these multicomponent glasses is crucial for advancing optical fiber technology, yet it remains challenging. This challenge is exacerbated by inherent difficulties in resolving complex atomic‐scale structures. This study leverages the mixed alkali effect to co‐tune the refractive index and crystallization resistance in fluorozirconate glasses is enhanced via Li + –Pb 2+ synergy, resulting in glass compositions with a tunable refractive index (1.49–1.53) while maintaining high thermal stability (Δ T > 75°C). Crucially, by combining first‐principle simulations with nuclear magnetic resonance and Raman spectroscopy, this study reveals the unique synergistic mechanism between Li + and Pb 2+ cations at the atomic scale. This synergy simultaneously promotes the breaking of Zr–F–Zr bridge bonds (generating non‐bridging fluorine and thereby lowering the glass transition temperature, T g ) and inhibits the ordering of Zr‐centered polyhedra (increasing viscosity and reducing the tendency to crystallize). This study explains the enhanced stability of glass at the atomic scale, which makes it possible to achieve both a tunable refractive index and crystallization resistance. This study provides a methodology for designing high‐performance fluoride optical fibers and advances the fundamental understanding of structure–property relationships in multicomponent fluoride glasses.