{\textit 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 were performed on a glass-based composite with nanometer-sized gallium oxide aggregates embedded in a potassium-silicate host glass. The aim of our studies was to advance the understanding of pressure-driven structural transformations in the glass matrix of the composite. Throughout the studied pressure range the Raman spectra confirmed that the glass matrix undergoes a range of structural transformations comparable to that reported previously for a pure SiO$_{2}$ glass. Compression from ambient up to 10.8 GPa 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 and a permanent reduction in SiO$_{4}$ ring statistics toward smaller than six-ring configurations and a coordination change of the silicon atom. The overall spectral profile at the end of the decompression cycle indicated the occurrence of permanent reconstructive structural changes in the glass matrix.