A Mask-and-Collapse Mechanism in Glass Degradation Driven by Percolation in Titanium Doped Fluoro-Borate System

Abstract This comprehensive study examines the effects of TiO2 incorporation (0-10 mol%) into a complex fluoro-borate glass system with the composition 55B₂O₃ - 15Na₂O - 5CaO - 5ZnO - 5MgF₂ - 5SrF₂ - (10-X)Li₂O - (X) TiO₂ mol% prepared by the melt quenching technique. Through integrated structural, mechanical, physical, and optical characterizations, the study reveals the dual-role of titanium ions as both a network modifier and disruptor. The novelty of this work lies in uncovering a critical "masking effect," where fluoride ions (F⁻) initially shield the glass network from the full disruptive impact of Ti⁴⁺ at low concentrations (X < 5 mol%), creating a "competitive equilibrium." The XRD proved the amorphous nature of the prepared system. It exhibits a significant drop in tetrahedral boron coordination (N4%) from 23.71% to 7.85%, indicating considerable network depolymerization. Beyond this threshold, a second novel mechanism is identified: a percolation-driven collapse, where Ti⁴⁺ ions form interconnected clusters that catastrophically amplify their depolymerising effects, decreasing N4% to 7.85% at X = 10 mol%. According to TCT, the mechanical properties show that the system's stability relies entirely on compensatory mechanisms until it is overwhelmed at X ≤ 7.5 mol%, after which the Young's modulus decreases. According to (MRN), the non-monotonic increase in density behaviour is observed, with a peak at X=7.5 mol% (2.833 g/cm³), as well as a drop in molar volume at the same point. The systematic reduction in the optical bandgap from 3.344 eV to 2.795 eV (direct) and 2.669 eV to 1.766 eV (indirect), alongside an increase in Urbach energy, describes the induced disorder. This fundamental understanding of competitive ion interactions and percolation thresholds provides a novel framework for designing advanced optical materials with customised properties for photonic applications.