Review of the structure, connectivity and preferential bonding in (alumino)borosilicate glasses: insights from infrared, Raman and NMR spectroscopy

This study revisits structural connectivities and bonding preferences in alkali borosilicate and aluminoborosilicate glasses based on 25 years of research of the corresponding author, using a combination of infrared, Raman and, with various collaborators, also solid-state NMR spectroscopy. Three representative systems, low-alkali NBS2, high-alkali MBS1 with M=Li to Cs, and high-Al 2 O 3 NABS, were examined to assess the validity and extrapolation of the Dell–Bray–Yun–Xiao (DBYX) model. While the model accurately predicts the fraction of tetrahedral boron, BO 4 – , across compositions, spectroscopic evidence reveals different connectivities for low R and high R values. NBS2 shows a shift from Si–O–B 4 to B–O–B linkages upon annealing, whereas MBS1 displays, as predicted, enhanced mixed bonds, including mixed-ring structures. The ring types, as well as packing density, depends on the modifier cation and its radius. In NABS, Al 2 O 3 wins the competition for Na 2 O for charge compensation, reducing BO 4 – formation. High aluminium content (Al 2 O 3 >10 mol%) leads to fewer mixed Si–O–B 4 bonds. Fewer mixed bonds are also observed for borosilicate glasses with low alkali content, where often 1–2 mol% aluminium oxide are added to prevent phase separation. This review discusses how glass composition, modifier field strength, charge-compensation competition, geometric factors, and thermal history all influence network connectivity and structure–property relation-