Real-Space Mapping of Oxygen Coordination in Phase-Separated Aluminosilicate Glass: Implication for Glass Stability

Understanding atomic arrangement in network glass is crucial to develop new glassy materials for future applications in medicine, optics, and electronics. While nuclear magnetic resonance (NMR) and X-ray total scattering are widely used for structural analysis, they provide limited information to correlate the atomic short-range orders with nanostructures in glasses such as phase separation and chemical heterogeneity. We recorded vibrational spectra in the Al- and Si-rich regions in a phase-separated aluminosilicate glass with electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). We observed an approximate to 7 meV energy shift of the Si-O stretching mode between two phases, which was confirmed by first-principles calculation due to change of O coordination. For the first time, the distribution of triply coordinated O (O-[3]) in network glasses was revealed. The O-[3] mapping may represent a tool to evaluate local glass-formability, which may be further applied to trace the crystallization path or local network densification.