Microscopic mechanism of structural and volume relaxation below glass
transition temperature in a soda-lime silicate glass revealed by Raman
spectroscopy and its first principle calculations
To elucidate the atomistic origin of volume relaxation in soda-lime silicate
glass annealed below the glass transition temperature (Tg), the experimental
and calculated Raman spectra were compared. By decomposing the calculated Raman
spectra into a specific group of atoms, we found that the Raman peak at 1050
cm-1 corresponds to bridging oxygen with a small Si-O-Si bond angle. The
experimental Raman spectra indicated that, during annealing below Tg, a
homogenization reaction Q2+Q4->2Q3 proceeds in the early stage of structural
relaxation. Then, the Si-O-Si units with relatively small angles decrease even
in the later stages, which is first evidence of ring deformation causing volume
relaxation of soda-lime silicate glass because decreasing small Si-O-Si angles
corresponds to the reduce of acute O-O-O angle in a ring and can expand the
space inside the rings, and Na can be inserted into the ring center. In
conclusion the ring deformation and Na displacement is the origin of the volume
relaxation of soda-lime silicate glass below Tg.Comment: 15 figures and 1 table for main text, 8 figures and 1 table for
supplemental inf