Structural Responses of Aluminoborosilicate Glasses to Pressure and Iodine Incorporation: An Advanced NMR Investigation

ABSTRACT Iodine‐129 is a critical challenge for nuclear waste immobilization due to its high mobility and extremely long half‐life (1.57 × 10 7 years). Although high‐pressure glass synthesis has been shown to significantly enhance iodine solubility, the structural mechanisms governing its incorporation are only partially understood. Here, we combine advanced multinuclear solid‐state NMR spectroscopy ( 11 B, 17 O, 23 Na, 27 Al, and 29 Si) with molecular dynamics and DFT calculations of NMR interactions to disentangle the respective roles of pressure and iodine incorporation in doubly isotopically enriched ( 17 O and 29 Si) aluminoborosilicate glasses synthesized at 1 and 2 GPa. NMR results show that iodine incorporation increases network polymerization primarily through the consumption of Si non‐bridging oxygens and the formation of additional Si–O–Si and Si–O–B linkages, whereas pressure independently promotes densification via enhanced BO 4 formation and stabilization of higher‐coordinated aluminum species. Notably, 17 O MAS, 3QMAS, and heteronuclear correlation experiments provide novel atomic‐scale insights into oxygen speciation in high‐pressure aluminoborosilicate glasses, a regime poorly documented. MD‐derived structural models reproduce pressure‐induced trends and enable quantitative interpretation of NMR data. These results establish a mechanistic framework for iodine incorporation under high‐pressure vitrification and help of designing advanced glass matrices for long‐term 1 2 9 I immobilization.