Pressure-Induced Densification of Oxide Glasses at the Glass Transition

Abstract

Densification of oxide glasses at the glass transition offers a novel route to develop bulk glasses with tailored properties for emerging applications. Such densification can be achieved in the technologically relevant pressure regime of up to ~1 GPa. However, the present understanding of the composition-structure-property relationships governing these glasses is limited, with key questions, e.g., related to densification mechanism, remaining largely unanswered. Recent advances in structural characterization tools and high-pressure apparatuses have prompted new research efforts. Here, we review this recent progress and the insights gained in the understanding of the influence of isostatic compression at elevated temperature (so-called hot compression) on the compositionstructure-property relationships of oxide glasses. We focus on compression at temperatures at or around the glass transition temperature (Tg), with relevant comparisons made to glasses prepared by pressure quenching and cold compression. We show that permanent densification at 1 GPa sets in at temperatures above 0.7Tg and the degree of densification increases with increasing compression temperature and time, until attaining an approximately constant value for temperatures above Tg. For glasses compressed at the same temperature/pressure conditions, we demonstrate direct relations between the degree of volume densification and the pressure-induced change in micromechanical properties such as hardness, elastic moduli, and extent of the indentation size effect across a variety of glass families. Finally, we review the results on relaxation behavior of hot-compressed glasses. In summary, all the pressure-induced changes in the structure and properties exhibit strong composition dependence. The experimental results highlight new opportunities for future investigation and identify research challenges that need to be overcome to advance the field.

Elasticity, hardness, and fracture toughness of sodium aluminoborosilicate glasses

“…This agrees with the positive correlation between E and C g reported for a wide range of different materials including oxide, oxynitride, and metallic glasses . Furthermore, it is known that both hardness and elastic moduli increase linearly with increasing density upon isostatic pressure treatment …”

Correlation between glass transition temperature and the width of the glass transition interval

“…As far as we are aware so far no comprehensive experimental investigations have been performed in order to analyze the dependence of vitrification parameters on the rate of change of pressure. Such approach seems to us to represent a very useful alternative tool in varying the properties of glasses like the change of the glass transition temperature by pressure or pressure‐induced densification of glasses similar to vitrification in cooling…”

Permanent Densification of Calcium Aluminophosphate Glasses

“…As a glass is compressed, the ionic environments can change in different ways, including a coordination number increase, a change in bond distances, angles, and in the types and amounts of linkages present (e.g., P-O-Al, P-O-P). In the case of Al, the most obvious structural change is an increase in coordination number, as observed in various oxide glasses (Allwardt et al, 2004;Kapoor et al, 2017c). The comparative abundance of each aluminum species is proportional to the area under its peak and the fitted values are given in Table 3.…”

“…The application of pressure enables tuning of the interatomic distances and bonding patterns in glassy solids (Kapoor et al, 2017c), providing an additional degree of freedom for altering glass properties compared to varying composition or temperature alone. Understanding the gradual or abrupt densification mechanisms involving various structural transitions is thus an important task in glass science and engineering, but it is complicated by the intrinsic atomic-scale disorder in glasses and the experimental difficulties in undertaking in situ high-pressure characterization experiments (Huang and Kieffer, 2004).…”

“…However, it is challenging to understand these interactions unambiguously in complex multicomponent oxide glasses. Furthermore, most of the highpressure investigations have focused on aluminoborosilicate glasses with relevance for the geological sciences (Kapoor et al, 2017c), while only relatively few studies have explored the pressure-induced changes in structure and properties of P 2 O 5containing glasses (Hirao et al, 1991;Mosey et al, 2005;Gauvin et al, 2007Gauvin et al, , 2013Yue et al, 2007;Brazhkin et al, 2011Brazhkin et al, , 2014Premila et al, 2012;Kapoor et al, 2017b;Shi et al, 2018). These previous studies reveal that the response of P 2 O 5 -based glasses toward high pressure treatment depends on the glass composition and the utilized compression route (e.g., cold vs. hot compression).…”