Sodium migration pathways in multicomponent silicate glasses: Car-Parrinello molecular dynamics simulations

Area of Science:

• Materials Science
• Solid State Chemistry
• Computational Materials Science

Background:

• Sodium migration in glasses is vital for biomedical applications.
• Understanding ion transport in low-silica alkali-alkaline earth silicate glasses is critical.
• Existing models often focus on higher-silica or mixed-alkali systems.

Purpose of the Study:

• To elucidate the mechanism of sodium migration in low-silica alkali-alkaline earth silicate glasses.
• To investigate the role of network flexibility and cation interactions in ion transport.
• To compare migration pathways with those in mixed-alkali and higher-silica glasses.

Main Methods:

• Car-Parrinello molecular dynamics (MD) simulations were employed.
• Analysis of MD trajectories using space and time correlation functions.
• Investigated cation site selectivity and network dynamics.

Main Results:

• Identified a complex sodium migration mechanism with unique features compared to other silicate glasses.
• Demonstrated that sodium cations exhibit low site selectivity, utilizing both Na and Ca sites.
• Revealed an additional migration pathway enabled by silicate network flexibility and transient site creation.
• Showed that sodium migration occurs between corner-sharing polyhedra, minimizing energy costs.

Conclusions:

• Sodium migration in these glasses is facilitated by a flexible silicate network and the participation of calcium ions.
• The low-silica composition and network structure promote efficient sodium transport, even in the presence of calcium.
• Findings provide insights into glass properties relevant for biomedical applications.