In situ Raman scattering studies of high-pressure stability and transformations in the matrix of a nanostructured glass-ceramic composite

High-pressure Raman scattering studies have been performed on a glass-based composite consisting of nanometer-sized gallium oxide aggregates embedded in a potassium-silicate host glass using the diamond anvil cell technique. The Raman spectra of this heterophase nanocomposite showed a range of pressure-induced structural transformations occurring in the glass matrix. Compression from ambient pressure up to 10.8 GPa indicated a progressive reduction in the width of the intertetrahedral Si-O-Si angle distribution, which was completely reversible on decompression to ambient pressure. At higher pressures, the Raman spectra demonstrated a breakdown of the intermediate-range order in the glass matrix of the nanocomposite. The enhancement of scattering intensity in the region of the D-defect band at 565 cm(-1) together with the blue shift of the main Si-O-Si symmetric stretching wavenumber are evidence of a permanent reduction in SiO4 ring statistics toward smaller-than-six-ring configurations in the three-dimensional glass network. Starting from 13 GPa, the Raman spectra displayed a remarkable decrease in the scattering intensity of the Si-O-Si symmetric stretching that has been related to a coordination change of the silicon atom. The Raman spectrum of the composite quenched from 23 GPa to ambient conditions illustrated the pressure-driven, permanent reconstructive modification of the glass matrix in the nanocomposite. The pressure-induced evolution of the Raman peaks assigned to the gallium oxide phase indicated a progressive densification of the nanocrystalline phase, reversible on decompression to ambient pressure. Copyright (c) 2005 John Wiley & Sons, Ltd.