Influence of modifier cation size on the structure and properties of boro‐aluminosilicate display substrate glasses

Abstract In alkali‐free aluminosilicate glasses, alkaline earth metal cations serve either as charge compensators for [AlO 4 ] − units or as network modifiers by disrupting the silicon‒oxygen network to generate non‐bridging oxygens, and/or by facilitating the transformation from [BO 3 ] to [BO 4 ]. The preference of different alkaline earth cations for either charge compensation or network modification is influenced by their ionic sizes and charge density, also known as cation field strength. This study investigates how variations in the mean modifier cation size (MCS) affect the structural and property changes in boro‐aluminosilicate glasses. Using Magic Angle Spinning Nuclear Magnetic Resonance (MAS‐NMR analysis of 29 Si, 27 Al, and 11 B, together with Raman spectroscopy and X‐ray photo‐electron spectroscopy measurements (Al 2p and B 1s ), we examine structural changes related to MCS and compare well‐annealed glass samples with those rapidly quenched in water. Our findings reveal a negative correlation between the Q 4 species in the silicon group and the [BO 4 ] fraction in the boron group as a function of MCS. [AlO 4 ] species dominates in local structure of Al, with minor [AlO 5 ] species found in samples of smaller cation, especially for magnesium containing one. Smaller cation, especially for Mg 2+ ion, acts less as a compensator for [AlO 4 ] and [BO 4 ] − , and less as a modifier to Si group than larger cations, and it leads to more disturbed [AlO 4 ] units and a pronounced non‐uniform structure. Mechanical and thermodynamic properties of glass show a decreasing trend with increasing MCS. Viscosity measurements are employed to explore how liquid fragility varies with the MCS. However, a higher fragility index, indicating a more “fragile” liquid is found for glasses with smaller MCS. The contrasting behavior between bulk glass and molten glass may be attributed to differences in effective network connectivity.