Ionic diffusion and the topological origin of fragility in silicate glasses

Area of Science:

• Materials Science
• Solid State Chemistry
• Physical Chemistry

Background:

• Mass transport in liquids and glasses is intrinsically linked to the structure and topology of their disordered networks.
• Understanding this relationship is key to developing new materials with tailored properties.

Purpose of the Study:

• To investigate the relationship between ionic diffusivity, fragility, and network structure in iron-bearing silicate glasses.
• To explore how different alkali and alkaline earth cations influence mass transport and glass properties.

Main Methods:

• Ionic diffusivity and fragility measurements were performed on a series of silicate glasses with varying alkali and alkaline earth cations.
• Diffusion studies were conducted around the glass transition temperature (Tg) under a reducing atmosphere.
• A topological model was developed to correlate fragility index (m) and Tg.

Main Results:

• Calcium ions (Ca2+) exhibited faster diffusion than alkali ions in SiO2-CaO-Fe2O3-A2O glasses.
• The activation energy for Ca2+ diffusion decreased with increasing alkali ion size, correlating with decreased liquid fragility.
• The developed model accurately predicted the relationship between fragility and Tg, with an exception for MgO-containing glass due to Mg2+'s unique role.

Conclusions:

• The study establishes a correlation between ionic diffusion, liquid fragility, and glass network topology.
• A novel model effectively links fragility and glass transition temperature based on topological considerations.
• The findings highlight the significant influence of specific cations, like Mg2+, on glass network structure and transport properties.