Low-frequency Raman scattering of magnesium aluminosilicate glasses and glass-ceramics

The evolution of low-frequeucy (<100 cm(-1)) Raman scattering of titania-co ntaining magnesium aluminosilicate (20MgO:20Al(2)O(3):60SiO(2) with 10 mol% TiO2) glasses with heat-treatment has been studied. It was found that in s pectra of heat-treated basses the intensity of the boson peak is rapidly di minished. Under certain conditions of heat-treatment schedules the boson pe ak disappears while the sample remains amorphous. It implies that sometimes the boson peak is missing from spectra of amorphous materials. III Raman s pectra of heat-treated glasses that show the disappearance of :he boson pea k a new narrow highly polarized low-frequency band appears and increases il l intensity. This band has been associated with a spheroidal mode of elasti c vibrations in nanometer sized particles of aluminomagnesium phase formed upon phase decomposition of the glass. Its frequency changes with heat-trea tment in the temperature range 750-950<degrees>C, from 50 to 17 cm(-1) refl ecting an increase in the sizes of corresponding nanometer particles. The c omposition and structure of amorphous and crystalline phases formed upon he at-treatment and also of residual glass as well were analyzed using the Ram an scattering data, small angie X-ray scattering (SAXS) and X-ray diffracti on (XRD) analysis. (C) 2001 Elsevier Science B.V. All rights reserved.