Raman scattering and molecular dynamics investigation of lead metasilicate glass and supercooled liquid structures

In this research we correlate the structural parameters obtained from molecular dynamics (MD) simulations and Raman scattering to construct a self-consistent picture of the glass structure, and its variation from ambient temperature to the supercooled liquid above the glass transition temperature (Tg). The MD results show that the glass structure is composed of SiO4 tetrahedra and PbOx (x = 4, 5) polyhedra. To correlate the Q(n) population obtained from the MD and Raman a second type of Q(3) species is required. The two types of Q(3) species are interpreted as being associated with the bimodal distribution displayed by the Pb-Si pair correlation function. From a MD snapshot is also shown that the second Q(3) species can have a bridging oxygen bound to a Pb ion. As the temperature increases, depolymerization of the Q(n) speciation is observed and confirmed by the oxygen speciation determined from both Raman and MD. The depolymerization of the silica network is consistent with the non-Arrhenian (fragile) viscosity decrease with temperature and may explain this viscosity behavior.