Role of Al formers and Na modifiers in Al₂O₃-SiO ₂-Na₂O-MgO-Eu₂O₃ glasses: Brillouin and Raman spectroscopy studies

Brillouin and Raman spectroscopies were used to investigate the structure of xAl₂O₃. (72.08-x) SiO₂. 14.81 Na ₂O.11.85 MgO.1.26 Eu₂O₃ (x=0, 2.96, 5.92, 8.88, 14.81 mol%; and yNa₂O. (83.93-y) SiO₂. 2-96 Al ₂O₃.11.85 MgO.1.26 Eu₂O₃ (y=9.86, 14.81, 19.73, 24.67 mol%) glasses. The depolymerisation (polymerisation) of the Eu³⁺ doped soda magnesia aluminosilicate (EDSMAS) glass is mainly characterised by the presence of nonbridging (bridging) oxygens and three (four) member silicate and aluminosilicate rings. The aluminium formers entering the glass recover Si-O-Si bridges by attracting charge balancing modifiers from depolymerised SiO₄ network. In this way the (Si,Al)₄ rather than (Si,Al)₃ membered rings are formed, i.e. the overall structure becomes more polymerised rather than fragmented. This is supported by the glass elastic constants and moduli as measured by Brillouin spectroscopy. Concurrent increasing polarisability deduced from the enhanced Poisson's ratio is mostly due to the appearance of AlO₄ tetrahedral groups weakly bound to sodium ions. The sodium modifier ions substituting for silicon atoms depolymerise the glass causing the formation of distinct Q³ and Q² species and the rapid increase in the number of three member rings. However, the overall glass structure becomes less compressible in the volumetric sense.