Journal of Non-Crystalline Solids 581 (2022) 121398 0022-3093/© 2022 Elsevier B.V. All rights reserved. Study of dynamics and structure in sodium silicate glasses. Molecular dynamics simulation. L.T. San d , N.V. Yen a, b, * , N.T. Thao c , P.K. Hung d , Fumiya Noritake e a Institute of Theoretical and Applied Research, Duy Tan University, Hanoi 100000 Vietnam b Faculty of Natural Sciences, Duy Tan University, Da Nang 550000, Vietnam c Faculty of Physics, Hanoi National University of Education, Vietnam d Institute of Engineering Physics, Hanoi University of Science and Technology, Vietnam e Graduate Faculty of Interdisciplinary Research, University of Yamanashi, Japan A R T I C L E INFO Keywords: sodium-silicate Voronoi polyhedron structure and dynamics correlation effect preferential diffusion path ABSTRACT We conduct molecular dynamics simulations to study dynamics and structure of sodium silicate glasses through Voronoi polyhedron and diffusion path consisting of Ox-polyhedrons connected via XY-lines. The result shows that Six-polyhedrons and the number of Ox-polyhedrons do not contain Na. Most of NBFx-polyhedrons contain 1, 2 or not Na, where BO, NBF is the O bonded with 2 and 1 or not Si, respectively. Average volume per polyhedron increases in order: Six-polyhedron → BOx-polyhedron → NBFx-polyhedron. Na atoms are concentrated 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 NBFx-polyhedron is larger than that around BOx- polyhedron. Major Na atoms move over BN- and NN-lines connecting with NBFx-polyhedrons. Moreover, Na atoms displace through the preferential diffusion path comprising mainly of NBFx-polyhedrons. The correlation effect is signifcant for sodium diffusion. 1. INTRODUCTION Silicate glasses are typically manufactured as window glasses for buildings and automobiles and display glasses for TV panels and mobile phones. They have varying physicochemical properties such as the melting point, glass transition temperature, viscoelasticity, thermal expansion and chemical durability with addition of the other network forming cations such as boron or aluminum ions, and the network modifers, namely, alkali metal or alkali earth metal ions [1,2]. Further, they are in the focus of many scientifc studies in recent years [3-7]. The X-ray electronic and magnetic nuclear resonance spectroscopy provide experimental verifcation of site specifcity like Na, K, Ca, Mg, bridging oxygen (BO) and non-bridging oxygen (NBO) [8-10]. In following BO, NBO and FO is denoted to oxygen bonded with 2, 1 and not Si, respec- tively. Due to the conventional experiments do not provide a direct and full access to the atomistic structure, the simulations are widely used to study glass materials [11-13] offering useful details about the structure as well as certain physical properties of those materials. Alkali silicate glasses are of scientifc interest for ionic transport properties [14-15], for example, the dynamics in them features very fast diffusivity of alkali that exceeds the one of Si and O by orders of mag- nitudes [16-18]. Such a high mobility of alkali is interpreted by the fact that alkali ions move in preferential diffusion pathway [19-22], namely, according to quasi-elastic neutron scattering experiments, the alkali ions diffuse via alkali rich channel in the relative immobile Si-O matrix, and a pre-peak around 0.9 Å 1 in the structure factor is found to relating with sodium rich channel. The molecular structure of silicate liquid and glass has been well described by the modifed random network model [23-25], which involves two interlacing disordered sub-regions, one of which contains the polymerized silica skeleton (covalent network), while the another comprises of large concentrations of modifers such as alkali (ionic channel). The alkali ions break the inter-tetrahedral bond and segregate into clusters which become continuous channels when their concentration reaches the percolation threshold [24-27]. Molecu- lar dynamics (MD) simulation [28-31] demonstrates the existence of Si-rich regions, and that the sodium trajectories form a well-connected network of pockets and pathways intimately related to the location of NBO. Moreover, the preferential diffusion pathway occupies the rela- tively small subspace of the system. Sodium silicate glass is the arche- typal glass forming system. The BO in this glass is either two-fold * Corresponding author. E-mail address: nguyenvanyen@duytan.edu.vn (N.V. Yen). Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol https://doi.org/10.1016/j.jnoncrysol.2022.121398 Received 14 November 2021; Received in revised form 27 December 2021; Accepted 3 January 2022