Medium-density amorphous ice

Amorphous ices govern a range of cosmological processes and are potentially key materials for explaining the anomalies of liquid water. A substantial density gap between low-density and high-density amorphous ice with liquid water in the middle is a cornerstone of our current understanding of water. However, we show that ball milling ordinary ice Ih at low temperature gives a structurally distinct medium-density amorphous ice (MDA) within this density gap. These results raise the possibility that MDA is the true glassy state of liquid water or alternatively a heavily sheared crystalline state. Notably, the compression of MDA at low temperature leads to a sharp increase of its recrystallization enthalpy, highlighting that H2O can be a high-energy geophysical material.

Automated summary

Amorphous ices are important for cosmological processes and understanding liquid water anomalies. A new medium-density amorphous ice (MDA) has been discovered through ball milling ordinary ice Ih at low temperature. This raises the possibility that MDA is the true glassy state of liquid water or a sheared crystalline state. Moreover, the high-energy recrystallization behavior of MDA at low temperature highlights the potential of H2O as a geophysical material.