High-pressure densification of fluoride, GeS₂ and silicate glasses

Densification of glasses having different chemical-bond properties and also different structures have been examined by treating ionic ZrF₄-based fluoride glasses, mixed ionic and covalent SiO₂-based oxide glasses, and a covalent GeS₂ sulfide glass at temperatures of about three-quarters of their respective glass-transition temperatures under pressures up to 9 GPa. The densities of GeS₂ glass and silicate glasses of SiO₂ contents > 50 mol% increased with increasing applied pressure. In ZrF₄-based glasses and silicate glasses with SiO₂ contents <50 mol%, on the other hand, the densities increased until an applied pressure around 3 GPa, the maximum densities were measured at pressures around 3 GPa, and then decreased with increasing pressure. The pressure dependences of permanent densification observed in the latter glasses are a permanent densification that has not been reported to our knowledge.