Influence of Magnesium on the Structure of Complex Multicomponent Silicates: Insights from Molecular Simulations and Neutron Scattering Experiments

Abstract

A series of multicomponent glasses containing up to five oxides are studied using classical molecular dynamics simulations and neutron scattering experiments. The focus is on the role of magnesium in determining the structural properties of these glasses and the possible mixed effect during a sodium/ magnesium substitution. Calculated structure functions (pair correlation function and structure factor) rather accurately reproduce their experimental counterpart, and we show that more fine structural features are qualitatively reproduced well, despite some discrepancies in the preferential spatial distribution between sodium and magnesium to aluminum and boron, as well as the nonbridging oxygen, distribution. The simulated systems offer a solid basis to support previous experimental findings on the composition−structure relationship, allowing for further analysis and property calculation. It is confirmed that the substitution of sodium by magnesium leads to the decrease of four-fold boron and a modification of the alkali coordinations with a significant change of the network structure. Specifically, magnesium coordination extracted from numerical simulations highlights a potential dissociation from penta-to tetra-and hexahedral units with increasing MgO contents along the glass series, which could not be resolved experimentally.

Effect of modifier cation field strength on the structures of magnesium oxide containing aluminoborosilicate glasses

“…On the other hand, MD simulations with the Wang et al. potential set 53 by Bisbrouck et al 35 significantly overestimate boron N 4 in all the glass compositions by 20%–30% as compared to NMR results. Furthermore, it is worth noting that the modified YDB model for aluminoborosilicate glasses 29,78 predicts constant boron N 4 values for several compositions (Table 7) as the model assumes that all alkali earth or alkali oxide modifiers have the same effect of charge compensation and to convert [3] B to [4] B.…”

“…The effect of the CFS was studied in terms of the change in coordination of the glass formers specially boron N 4 and also on different short‐ and medium‐range structure features. The results from our simulations are compared with those from recent experimental (NMR) 32 and simulations 35 . The results show that the oxygen coordination of Si 4+ remained fourfold coordinated, not affected by the composition change.…”

“…(The boron N 4 value from YDB model calculated in Ref. [35] shows large variations, which might be due to wrong assumptions for compositions with alumina.) This assumption is incorrect as found in recent NMR studies 21,32 .…”

“…One common definition of CFS is the ratio of the formal charge of the cation to the cation–oxygen bond distance squared. It is observed that cations with higher field strength tend to promote the formation of fivefold coordinated Al and threefold coordinated B 21,32‐35 . By performing NMR study on series of Mg, Ca, Sr, Ba, K, Na containing aluminoborosilicate glasses, Yamashita et al 36 .…”

“…In this work, a series of aluminoborosilicate glasses with fixed glass former percentage but different mixings of modifier cations with different field strengths have been studied using MD simulations with the recent developed composition‐dependent partial charge potentials 52 . The obtained results are compared with experimental findings from NMR and Raman spectroscopy, 32 as well as with results from other MD simulations, 35 to discuss the effect of CFS on the glass structures and the structural role of MgO in these glasses.…”