Low-density amorphous ice contains crystalline ice grains

Ice on Earth typically adopts a neatly arranged hexagonal crystalline structure. A range of amorphous ices—solids without long-range order—also exist. The oldest known form is called low-density amorphous (LDA) ice. LDA has traditionally been viewed as a “snapshot of liquid water”.

Now, scientists have discovered tiny crystallites embedded within this amorphous material. They used two computer models to determine the structure of LDA: One model explored the solidification of ice from liquid water, while the other depicted the breakdown of crystallite domains towards an amorphous state. Neither model reproduced a fully disordered amorphous solid, but was instead interrupted by the presence of small ice crystals. In additional experimental work, the team recrystallized LDA made from different parent materials.

These experiments uncovered a “memory effect” with respect to the parent materials, again confirming the presence of the small crystals. The results add to the long-standing mystery of the amorphous ices and their role in understanding liquid water.

Authors: Michael Benedict Davies, Alexander Rosu-Finsen and Christoph G. Salzmann, Angelos Michaelides

DOI: https://doi.org/10.1103/PhysRevB.112.024203