Recently, the Department of Advanced Laser and Optoelectronic Functional Materials at the Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, revealed, on the atomic scale, how Al₂O₃ inhibits phase separation in NaPO₃–SiO₂ glasses, providing an important theoretical basis for designing functional glasses with high homogeneity and stability. The related results were published in The Journal of Physical Chemistry C under the title “Composition-Structure Correlations in Al₂O₃–NaPO₃–SiO₂ Mixed-Network Former Glasses: Insights from Advanced Solid-State NMR Spectroscopy”.

Phosphate-silicate mixed-network former glasses combine the low melting and high dopant capacity of phosphate glasses with the favorable thermal and chemical stability of silicate glasses, offering greater freedom for co-designing structure and properties. However, because different network formers differ in their local structures and bonding modes, phosphate-silicate glasses still suffer from insufficient resistance to hydrolysis, a tendency to phase separation, relatively poor thermal stability, and weak mechanical properties. Therefore, studying the microscopic structural rules of mixed-former glasses and revealing the intrinsic causes of their phase separation is important for the development of such functional glasses.

Using a suite of advanced solid-state NMR (SSNMR) techniques, this study elucidated how composition affects phase separation behavior in mixed-network former glasses. It was found that in the 80NaPO₃–20SiO₂ glass the network is dominated by homonuclear linkages such as Si–O–Si and P–O–P, with Na⁺ ions mainly concentrated in the phosphate phase, and significant phase separation present. With the addition of Al₂O₃, Al preferentially bonds with phosphate units to form Al–O–P linkages; when the average number of Al atoms bonded per P atom exceeds two, Al–O–Si linkages begin to increase markedly. This structural evolution drives part of the Na⁺ population to migrate from phosphate-rich regions into the silicate network and gradually form Si–O–Al–O–P connections, which effectively suppresses phase separation between different network formers and leads to a highly homogenized glass structure. The study thus clarifies the atomic-scale structural mechanism by which Al₂O₃ inhibits phase separation in mixed-network former glasses.

This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences [Grant No. XDB0650000].

Figure 1. Schematic diagram of the structural evolution of Al₂O₃−NaPO₃−SiO₂ glasses.

Original link：http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5c0735