Coordination Changes in Densified Aluminate Glass upon Compression up to 65 GPa: A View from Solid-State Nuclear Magnetic Resonance

Abstract

Deciphering the structural evolution in irreversibly densified oxide glasses is crucial for fabricating functional glasses with tunable properties and elucidating the nature of pressure-induced anomalous plastic deformation in glasses. High-resolution NMR spectroscopy quantifies atomic-level structural information on densified glasses; however, its application is limited to the low-pressure range due to technical challenges. Here, we report the first high-resolution NMR spectra of oxide glass compressed by diamond anvil cells at room temperature, extending the pressure record of such studies from 24 to 65 GPa. The results constrain the densification path through coordination transformation of Al cations. Based on a statistical thermodynamic model, the stepwise changes in the Al fractions of oxide glasses and the effects of network polymerization on the densification paths are quantified. These results extend the knowledge on densification of the previously unattainable pressure conditions and contribute to understanding the origin of mechanical strengthening of the glasses.

Structural Aspects of Ambient-Temperature Densification of Highly Crack-Resistant Borosilicate and Aluminoborosilicate Glasses: Two Case Studies Examined by Solid-State NMR

“…The response of glass properties to elevated pressure has been of great general fundamental and applied interest. − Owing to its element selectivity, local selectivity, and quantitative character, solid-state NMR has been playing an important role in characterizing structural changes upon pressurization, partly because it lends itself easily to structural interpretations of the observed spectroscopic changes. Accordingly, the literature presents structural NMR studies on a large variety of glasses that were pressurized near and above the glass transition temperature (“hot pressurization”). − In contrast, NMR studies on samples exposed to pressurization at ambient temperature (“cold pressurization”) are much more scarce and limited to only a few compositions. − Such studies may be particularly useful for learning about the mechanical failure of glasses upon impact, such as crack initiation and propagation, as the high pressure applied may mimic the structural effect occurring upon the initiation of radial cracks under high external loads. Identifying the local structural changes occurring under such conditions will be useful to characterize the ability of a glass network to undergo plastic deformation, which is an important feature for the compositional design of glasses with high impact stability. − According to previous studies on borosilicate and boroaluminosilicate glasses, resistance to crack initiation under indentation is very related to the degree of densification ability.…”