Atomistic origin of structural relaxation in lead metasilicate and lithium disilicate glasses.

A combination of density measurement, differential scanning calorimetry, refractometry, and Raman and 29Si nuclear magnetic resonance (NMR) spectroscopy is employed to characterize the evolution of the structure and physical properties of lithium disilicate (Li2Si2O5) and lead metasilicate (PbSiO3) glasses during physical aging. Both glasses display marked increase in density, enthalpy recovery, and refractive index following a temperature down‐jump near their glass transition regions. The collective analysis of Raman and NMR spectra reveals that the aging‐induced structural relaxation in these silicate networks involves a significant disproportionation of Q‐species as well as their spatial clustering. [ABSTRACT FROM AUTHOR]