Abstract:
Ultralow expansion (ULE) glass, a binary TiO2–SiO2 glass with 5.67 mol % TiO2, was exposed to microindentation. Vitreous silica was similarly treated and used as a reference material, including the characterization of mechanical properties by means of ultrasonic echography and nanoindentation. The structural modifications induced by indentation were analyzed by micro-Raman spectroscopy. The observed structural changes are consistent with an anomalous, densification-driven, deformation mechanism similar to those observed for vitreous silica or commercially relevant low alkali borosilicate glasses like Duran. As for these fully polymerized glasses, the Raman spectra of indents in the ULE glass are characterized by an upshift of the 407 cm–1 band and an increase in the intensity of the D1 and D2 defect bands, all consistent with structural rearrangements from mostly larger five- and six-member rings to a larger population of smaller four- and three-member rings and an overall lowering of the free volume in the glass. However, contrary to silicon, titanium may change its coordination number under the impact of microindentation. Raman spectra of selected reference materials such as TiO2 and BaTiO3, with known octahedral titanium coordination and known connectivity, as well as fresnoite Ba2TiSi2O8 with known fivefold Ti4+ coordination, are therefore included in this study in support of assigning the new activity appearing in the Raman spectra after an indentation of the ULE glass sample.
Description:
This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry: C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.0c09865.
