Atomistic mechanism of structural and volume relaxation below glass transition temperature in a soda-lime silicate glass revealed by Raman spectroscopy and its DFT calculations

T Suzuki and Y Hamada and M Shimizu and S Urata and Y Shimotsuma and K Miura, JOURNAL OF CHEMICAL PHYSICS, 160, 034501 (2024).

DOI: 10.1063/5.0181160

To elucidate the atomistic origin of volume relaxation in soda-lime silicate glass annealed below the glass transition temperature (T-g), the experimental and calculated Raman spectra were compared. By decomposing the calculated Raman spectra into specific groups of atoms, the Raman peaks at 800, 950, 1050, 1100, and 1150 cm(-1) were attributed to oxygen and silicon in Si-O-Si, non-bridging oxygen in the Q(2) unit, bridging oxygen in low-angle Si-O-Si, non-bridging oxygen in the Q(4) unit, and bridging oxygen in high-angle Si-O-Si, respectively. Based on these attributions, we found that by decreasing the fictive temperature by annealing below T-g - 70 K, a homogenization reaction Q(2) + Q(4) -> 2Q(3) and an increase in average Si-O-Si angle occurred simultaneously. By molecular dynamics simulation, we clarified how the experimentally demonstrated increase in average Si-O-Si angle contributes to volume shrinkage; increasing Si-O-Si angles can expand the space inside the rings, and Na can be inserted into the ring center.

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