Degree of Permanent Densification in Oxide Glasses upon Extreme Compression up to 24 GPa at Room Temperature

Abstract

During the decompression of plastically deformed glasses at room temperature, some aspects of irreversible densification may be preserved. This densification has been attributed primarily to topological changes in the glass networks. The changes in short-range structures like cation coordination numbers are often assumed to be relaxed upon decompression. Here, the NMR results for aluminosilicate glass upon permanent densification up to 24 GPa reveal the noticeable changes in the Al coordination number at pressure conditions as low as ~6 GPa. A drastic increase in highly coordinated Al fraction is evident over only a relatively narrow pressure range of up to ~12 GPa, above which the coordination change becomes negligible up to 24 GPa. In contrast, Si coordination environments do not change, highlighting preferential coordination transformation during deformation. The observed trend in the coordination environment shows a remarkable similarity with the pressure-induced changes in the residual glass density, yielding the predictive relationship between the irreversible densification and the detailed structures under extreme compression. The results open a way to access the nature of plastic deformation in complex glasses at room temperature.