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

The evolution of low-frequeucy (<100 cm(-1)) Raman scattering of titania-containing 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 spectra of heat-treated basses the intensity of the boson peak is rapidly diminished. Under certain conditions of heat-treatment schedules the boson peak disappears while the sample remains amorphous. It implies that sometimes the boson peak is missing from spectra of amorphous materials. III Raman spectra of heat-treated glasses that show the disappearance of the boson peak a new narrow highly polarized low-frequency band appears and increases in intensity. This band has been associated with a spheroidal mode of elastic vibrations in nanometer sized particles of aluminomagnesium phase formed upon phase decomposition of the glass. Its frequency changes with heat-treatment in the temperature range 750-950<degrees>C, from 50 to 17 cm(-1) reflecting an increase in the sizes of corresponding nanometer particles. The composition and structure of amorphous and crystalline phases formed upon heat-treatment and also of residual glass as well were analyzed using the Raman scattering data, small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) analysis. (C) 2001 Elsevier Science B.V. All rights reserved.