Study on Micro Structural Properties of Alkali - Doped SiO2 Melt Using Molecular Dynamics Simulation

Molecular dynamics (MD) simulation could provide details about local microstructure at atomic level, so we use this method to investigate micro-structural properties of sodium in Na2O-doped SiO2 melt. Additionally, we calculated the Voronoi polyhedrons to determine the spatial distribution of atoms in the simulation models. The result shows that many bridging oxygen (BO) polyhedrons and all Si-polyhedrons do not contain Na atoms. Most non-bridging oxygen (NBO) polyhedrons contain 2, 1 or no Na atoms, where BO, NBF is the O bonded with 2 and 1 or no Si, respectively. Average volume per polyhedron decreases in order: NBFx-polyhedron ® BOx-polyhedron ® Six-polyhedron. Na atoms are found in NBFx-polyhedrons and frequently move through them leading to very fast diffusivity of Na in comparison with Si and O. The simulation shows that the number of neighbors around the NBFx-polyhedron is larger than that around the BOx-polyhedron.