Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 243

At high degrees of supercooling, liquid–liquid phase transitions have been observed, a phenomenon now commonly referred to as polyamorphism ([26], Chapter 3.9). These phase transitions have been observed in water, supercooled oxides, semiconductors, and metallic alloys, leading to new types of glass, such as low‐ and high‐density amorphous phases – LDA and HDA respectively – each differing in density and entropy but sharing the same composition [1, 14, 21, 26].

In some multicomponent supercooled oxide liquids, on the other hand, atomic diffusion can result in the coexistence of liquids with different compositions, the analogue of multiple phases in crystalline systems. On cooling these lead to phase‐separated glasses (PSG) – the best‐known being borosilicates [7]. Pyrex, for example, combines low thermal expansion with high mechanical strength, whereas Vycor glass owes its special open microporous structure to the continuous silicate phase that is left when the borate phase has been leached out.

In summary, the extended structure of glass connects all of the various ordered regions present on different length scales and underpins the diverse global properties of the glassy state.