A critical evaluation of barium silicate glass network polymerization

Abstract

The state of polymerization in barium silicate glasses (xBaO·(1-x)SiO2, 0.28 ≤ x ≤ 0.45) has been studied by both experiment (Raman, static and MAS 29Si NMR spectroscopy) and molecular dynamics simulations (Vashishta-Rahman and Du-Cormack potentials). No a priori assumptions were made about the number of Qn species, specific mean polymerization nor presence or absence of ‘free’ oxygen species. This allowed us to test the relationships between these structural aspects.The Qn site interconversion equilibrium constants KQ2 and KQ3 were found to be 0.07 and 0.05±0.02 from static 29Si NMR, and 0.14±0.07 and 0.07±0.01 from 29Si MAS NMR, respectively. The Qn species distribution was used to determine the Raman scattering cross-sections for Q1, Q2 and Q3 as 1.01±0.15, ∼1.1, and 1.14±0.04, respectively, although some compositional dependence was found. The Q4 cross-section displays a unique behavior approaching 0 at 38% BaO. This more accurate structural framework paves the way for future studies to establish meaningful structure−property relationships for these glasses.