Effect of cation field strength (CFS) on Boro-aluminosilicate glasses

What is it about?

The glass system 65SiO2-11Al2O3-8B2O3-16RO (where R = Mg, Ca, Sr, Ba), used as a substrate material for thin-film transistor liquid crystal displays (TFT-LCDs), is investigated as a function of cation field strength (CFS). Cations with higher CFS, particularly Mg²⁺, exhibit inferior charge-compensating ability for [AlO₄]⁻ and [BO₄]⁻ units, resulting in the highest proportions of non-bridging oxygen-containing species such as [AlO₅] and trigonal [BO₃]. Additionally, their modifying effect on silicate network structures is weaker, leading to the segregation of Q⁴ units into more organized and highly polymerized structural domains. In samples containing cations of higher CFS, a pronounced structural inhomogeneity is observed, consisting of distinct structural units that are not randomly distributed at the atomic level. Instead, these units tend to cluster into phase-separated regions, as suggested by Raman spectroscopy. The relationship between liquid fragility and CFS is also examined, revealing that higher CFS correlates with increased fragility, as indicated by higher m values.

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Photo by Timothy Muza on Unsplash

Photo by Timothy Muza on Unsplash

Why is it important?

We have investigated the influence of alkaline earth modifier cations on the structure and properties of boro-aluminosilicate display substrate glasses. Cations with higher CFS, especially for Mg2+, act as worse compensators for [AlO4] and [BO4] than larger cations with lower CFS, and its modifying effect on Si group is also weaker. Although [AlO4] dominates the aluminium coordination environment across all samples,minor [AlO5] still can be observed in samples with small cations, especially for Mg2+. And a more disturbed [AlO4] units and a pronounced non-uniform sturcture is found in magnesium containing sample related to medium-range heterogeneity. A negative correlation between the Q4 species in the silicon group and the [BO4] fraction in the boron group can be found, with smaller cations exhibiting higher Q4 and lower [BO4]

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