Raman spectroscopic study of structural changes induced by micro-indentation in low alkali borosilicate glasses

• The effect of micro-indentation on local glass structure is studied.
• A scheme for indentation-induced structural changes is established.
• Indentation-induced structural changes are correlated to different deformation mechanisms.
• Deformation changes from density-driven (silica) to shear-driven (alkali-borate).

We report on the effect of micro-indentation on the local structure of glasses in the ternary borosilicate glass system Na2O–B2O3–SiO2. Indentation experiments were performed with loads ranging from 0.49 to 4.91 N and for loading times of 10–30 s in order to analyze the impact on the silicate and borate sub-networks in glasses ranging from pure SiO2 to binary Na2O–4B2O3, with a ratio of R = Na2O/B2O3 < 0.5. The Raman spectra reveal distinct changes in the glass structure, which can be correlated to different densification mechanisms occurring in the silicate and borate sub-networks, respectively. A clear trend from anomalous (densification-driven) deformation in silica-rich to normal (shear-driven) deformation behavior in alkali borate-rich glasses is observed.