Effect of lithium concentration on the network connectivity of nuclear waste glasses

• D-HMQC experiments suggests Li is in close proximity to BO 3 sites in all compositions • Li charge compensates [BO 4 ] − and [AlO 4 ] − sites at high Li concentrations • Li has a greater impact on the 7-oxide glass network Structure of borosilicate glasses with varying Li 2 O contents were investigated using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), employing 6 Li, 11 B, 23 Na, 27 Al and 29 Si nuclei. 11 B MAS NMR revealed that increasing Li 2 O contents result in formation of [BO 4 ] − sites at the expense of BO 3 . 11 B{ 6 Li} and 27 Al{ 6 Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed Li as a charge compensator for anionic tetrahedral sites with increased Li. 11 B{ 6 Li} J-coupling mediated HMQC NMR suggested the possible association of Li with non-bridging oxygens on Q 2 and Q 3 sites, indicating its dual role in the glass network. 29 Si and 23 Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased Li. NMR results are supported by Raman spectroscopy and thermal analysis that indicate depolymerisation of the silicate network and a reduction in glass transition temperature at higher Li content.