A Raman-spectroscopic study of indentation-induced structural changes in technical alkali-borosilicate glasses with varying silicate network connectivity

• Effect of micro-indentation on the local borosilicate glass structure.
• Glass structure probed by Raman and infrared spectroscopy
• NBO content controls the mechanisms of indent-induced structural changes.
• Deformation changes from density-driven (silica) to shear-driven (alkali-borate)

We report on the deformation behavior of a series of glasses in the ternary alkali-borosilicate system. Vickers indentation was applied to different samples and structural changes were studied by micro-Raman spectroscopy. Selected sodium- and potassium-borosilicate glasses, a soda-lime silicate glass and pure vitreous SiO2 were chosen as models for technical glasses, as their varying content of non-bridging oxygen atoms affects the connectivity of the silicate and borate sub-networks. Indentation experiments were performed with different loads and two different load times in order to analyze the response of the two sub-networks in the studied glasses.The measured Raman spectra show distinct indentation-induced changes in the glass structure. These changes depend not only on the borate concentration, but also on the silicate sub-network's connectivity and reflect anomalous (densification-driven) and normal (shear-driven) deformation mechanisms. Using vitreous SiO2 as reference material, indentation-induced structural changes were also correlated to hydrostatic compression experiments from the literature in order to develop a more detailed picture of the apparent evolution of the local compaction in and around the indent.