Synergistic Cr 2 O 3 –TiO 2 Effects on Network Depolymerization and Crystallization Kinetics in CaO–MgO–2SiO 2 Glass

ABSTRACT The silicate network and crystallization of Al‐free stoichiometric diopside (CaO–MgO–2SiO 2 , CM2S) glass co‐doped with Cr 2 O 3 and TiO 2 were studied using Raman spectroscopy, XPS, UV–Vis diffuse reflectance, and DTA. TiO 2 depolymerizes the glass network by increasing the proportion of Q 1 silicate units at the expense of Q 3 and Q 0 species. Ti 4+ ions exist mainly as five‐coordinated [TiO 5 ] polyhedra, which aid viscous sintering but destabilize the network at high doping levels. In the as‐quenched glasses, Cr exists as a mixture of Cr 3+ and Cr 6+ . Adding TiO 2 limits Cr 3+ oxidation, increases Cr 2 O 3 solubility, and stabilizes Cr 3+ in octahedral [CrO 6 ] sites. Kinetic analysis indicates a two‐stage crystallization process: initial heterogeneous surface nucleation followed by stress‐induced secondary crystallization. The co‐doping maintains the surface‐dominated crystallization mode of the base CM2S glass. However, TiO 2 significantly lowers the activation energy for secondary crystallization, accelerating the overall rate. Optimal densification is achieved at 3.60 wt% TiO 2 (CT3), balancing viscous flow against premature crystallization. Fundamentally, this work provides a theoretical framework for tailoring the sinter–crystallization coupling and Cr valence stabilization in Al‐free diopside‐based model systems.