Pressure-induced phase transformations in ice

Abstract

Using molecular-dynamics calculations, we show that at 80 K, ice Ih undergoes a transition to a high-density amorphous (hda) form at about 13 kbar. At higher pressures, the calculated oxygen atom radial distribution function shows strong resemblance to that of ice VIII. The most characteristic feature of hda ice, namely the peak observed around 3.5 Å in the oxygen radial distribution function, is ascribed to molecules occupying interstitial-like sites. On warming of a sample of hda ice recovered at zero pressure, the structure evolves to a lower-density form. These observations are in good accord with available experimental data.