IR and Raman spectroscopic study of some strontium aluminosilicate glasses

Abstract

Vibrational spectra are measured for strontium aluminosilicate glasses with the composition (in mol%) x SrO ∙ y AI2O3 ∙ (100-x-y) SiO2 (33 ≤ x ≤ 40, 0 ≤ y ≤ 2) with a water content ranging from 0.014 to 0.14 mol ∙ l-1 . The OH bands systematically change with glass composition in both MIR and NIR regions. The ratio of the absorption coefficients α3550/α2800 increases with decreasing number of nonbridging oxygens per tetrahedron (NBO/T; Τ = Si, AI). This indicates an increasing amount of strongly hydrogen bonded OH groups (2800 cm-1) with NBO/T relative to the weakly bonded hydroxyls (3550 cm-1) within the compositional series. Intensity changes in the Raman and IR reflectance spectra also reflect the substitution of Al3+ for Si4+ in the network and the incorporation of Sr2+. The increasing intensity ratio of the Raman bands I945/I1070 with NBO/T indicates an increase of structural units relative to Q^3, as well as the weak shoulder at 870 cm-1 shows a rising amount of Q units. The growing intensity of the IR reflectance band at 930 cm-1 with NBO/T confirms the increasing amount of nonbridging oxygen in the glasses. Α depolarized Raman band at 330 cm-1 was assigned to an Sr-O vibration. For hydrated samples the significantly higher ratio of α3550/α2800 in relation to the basic glasses can be explained by structural changes in the samples due to the water enrichment procedure. The hydroxyl content of the basic and hydrated glasses can be estimated by the so called two-band method with composition independent extinction coefficients for the two IR bands at about 3550 and 2800 cm-1, ε3550 = 80 1 ∙ mol-1 ∙ cm-1 and ε2800 = 170 1 ∙ mol-1 ∙ cm-1, independent of the Al3+ content of the glasses.