Raman and 27Al NMR structure investigations of aluminate glasses: (1 − x)Al2O3 − x MO, with M = Ca, Sr, Ba and 0.5 < x < 0.75)

Aluminate glasses are important materials from a fundamental structural point of view because Al is the only network former. They present also a technological interest because of their good IR transmission and ultralow optical losses. Aluminum in glasses of the system MO–Al2O3 (M = Ca, Sr, Ba) can have different coordination numbers, essentially 4 and 6, as a function of the MO/Al2O3 ratio. Using Raman spectroscopy and high field 27Al NMR spectroscopy, we have determined the structure of aluminum network as a function of MO/Al2O3 ratio with M corresponds to different alkaline–earth cations. Al is essentially in four-fold coordination with different amounts for Al2O3 between 50 and 75% but varies between Q2 and Q4 species as a function of MO/Al2O3 ratio where Q is tetrahedral species and n the number of bridging oxygen.