Atom Probe Tomography Investigation of Clustering in Model P2O5-Doped Borosilicate Glasses for Nuclear Waste Vitrification

Atom Probe Tomography (APT) has been utilised to investigate the microstructure of two model borosilicate glasses designed to understand the solubility limits of phosphorous pentoxide (P2O5). This component is found in certain high-level radioactive defence wastes destined for vitrification, where phase separation can potentially lead to a number of issues relating to the processing of the glass and its long-term chemical and structural stability. Development of suitable Focused Ion Beam (FIB)-preparation routes and APT analysis conditions were initially determined for the model glasses, before examining their detailed microstructures. In a 3.0 mol% % P2O5-doped glass, both visual inspection and sensitive statistical analysis of the APT data shows homogeneous microstructures, while raising the content to 4.0 mol% initiates formation of phosphorus-enriched nanoscale precipitates. This study confirms expected inhomogeneities and phase separation of these glasses, and offers routes to characterising these at near-atomic scale resolution using APT.