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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.

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We report on the effect of varying the Zn 2+ /Mg 2+ ratio on the structure and biodegradation of glasses in an alkali-free system designed in the glass forming region of diopside (CaMgSi 2 O 6 )-fluorapatite [Ca 5 (PO 4 ) 3 F]-TCP (3CaO$P 2 O 5 ). The zinc-containing glasses designed in the as-mentioned ternary system are potential materials for their application in bone regeneration and tissue engineering. The melt-quenched glasses with compositions (mol%), 36.07CaO À (19.24 À x) MgO À xZnO À 5.61P 2 O 5 À 38.49SiO 2 À 0.59CaF 2 , where x varies between 0 and 10, have been investigated for their structure by molecular dynamics simulations as well as by nuclear magnetic resonance spectroscopy. In all the investigated glasses silicate and phosphate components are mainly present as Q 2 (Si) and Q 0 (orthophosphate) species, respectively. Zinc retains structural features similar to magnesium, with predominant five-fold coordination. The apatite-forming ability of glasses has been investigated by X-ray diffraction and infrared spectroscopy after immersion of glass powders in simulated body fluids for time durations varying between 1 h and 7 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO-10993-14.The increasing Zn 2+ /Mg 2+ ratio decreases the chemical degradation of glasses as well as reducing their apatite forming ability. The results allowed us to discuss the biodegradation of alkali-free bioactive glasses on the basis of the structural role of zinc and magnesium.