Boron coordination structure at the surfaces of sodium borosilicate and aluminoborosilicate glasses by B K-edge NEXAFS

Understanding the impact of boron on glass surface properties is an ongoing challenge in the development of novel technical glasses. Prior work has shown that the behavior of boron is often linked to its structural coordination environment-a fact well-established in bulk glass properties, but also observed with surface reactivity. Here, we interrogate the coordination state of boron at the surfaces of a span of sodium borosilicate and boroaluminosilicate glasses using B K-edge NEXAFS spectroscopy. After considering both beam-damage and surface preparation effects, we examine results for surface coordination state as a function of composition, and contrast results against bulk coordination determined by B-11 NMR spectroscopy. Key results show deviation from the principles that govern bulk structure, with a preference to form 4-coordinated species at the surface-likely from interaction with ambient moisture-and correlated with the presence of 3-coordinated boron with NBO in the bulk.