Origin of the mixed alkali effect in silicate glass

Abstract

Silicate glasses have evolved from basic structural materials to enabling materials for advanced applications. In this article, we unravel the origin of the mixed alkali effect for alkali silicate 22.7R 2 O-77.3SiO 2 glasses (R = Na and/or K) by identifying the variation in the alkali ion location around the non-bridging oxygen atoms. To do so, we constructed a state-of-the art structural model, which reproduces both diffraction and NMR data with a particular focus on the behavior of the alkali ions. A novel topological analysis using persistent homology found that sodium-potassium silicate glass shows a significant reduction in large cavities as a result of the mixed alkali effect. Furthermore, a highly correlated pair arrangement between sodium and potassium ions around non-bridging oxygen atoms was identified. The potassium ions can be trapped in K-O polyhedra due to the increased bridging oxygen coordination; therefore, the correlated pair arrangement is likely the intrinsic origin of the mixed alkali effect.

Structural origins of the Mixed Alkali Effect in Alkali Aluminosilicate Glasses: Molecular Dynamics Study and its Assessment

“…When Na ions are replaced by K ions, the average size increases, in the case of the CS model. A similar behavior was recently observed for mixed Na and K silicate glasses 47 .…”

X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa

“…As revealed by SAXS, XRD, and ND, the hydrous glass synthesized in this study is a mixture of SiO 2 -rich glass parts and a D 2 O-rich domain. By assuming that the structure of each phase is the same as that for pure SiO 2 glass and pure liquid D 2 O, the S(Q) for hydrous glass can be calculated from those for pure phases [22,[33][34][35] (the detailed method is described in Appendix B). Comparison of the S X (Q) and the S N (Q) of the hydrous SiO 2 with those calculated from the previously reported S(Q) are shown in Figure 4.…”

“…In XRD, the S X (Q) of hydrous SiO2 glass changes with pressure in the same way as anhydrous SiO2 glass reported [22,34], and that simulated for the hydrous glass using them. (B) Corresponding S(Q) for neutron, S N (Q) [33,35]. (C) Comparison of the observed and simulated S X (Q)s for the hydrous SiO 2 glass.…”

Correlation between Structures and Physical Properties of Binary ZnO–P2O5 Glasses

“…[ 28,29 ] Unlike the neutron total structure factor S N ( Q ) shown in Figure 6a, the principal peak, [ 26 ] which reflects the packing of oxygen atoms, [ 27 ] is not observed in the X‐ray data (Figure 6b). [ 32 ] In the case of SiO 2 , a distinct FSDP is observed, whose periodicity and correlation length 2 π /Δ Q FSDP have been previously reported. [ 33,34 ] Although both SiO 2 and P 2 O 5 are simple glass‐forming oxides, the height and width of the FSDP are different due to the difference in the tetrahedra connectivity, because SiO 2 forms Q 4 networks, whereas P 2 O 5 forms Q 3 networks.…”

“…The constructed 3D networks also suggest that the intermediate structures vary depending on the chemical composition. In this study, we focus on two measurement techniques: Raman scattering for the boson peak [ 18–23 ] and the first sharp diffraction peak (FSDP) [ 23–34 ] in the neutron and X‐ray diffraction (XRD) data. Although it may be apparent that the boson peak is not directly related to the FSDP, [ 35 ] it is important to examine both sets of data.…”