Medium-density amorphous ice

The amorphous ices govern a wide range of cosmological processes and are potentially key materials for explaining the anomalies of liquid water. A substantial density gap between low-density amorphous (LDA) and the high-density amorphous ices (HDA) with liquid water in the middle is a cornerstone of our current understanding of water. However, here 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. Remarkably, 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.