The quest for the hydrogen-disordered counterpart of ice II

Water displays a highly complex phase diagram that is key to a range of critical processes, from the evolution of icy moons to that of the Earth's hydrosphere and even of life itself. Using ISIS facilities, our group has made tremendous progress exploring the phase diagram of ice. For example, we discovered three phases of ice labelled ices XIII, XIV and XV which are the hydrogen-ordered counterparts of ices V, XII and VI. This proposal focusses on ice II which is special in the sense that it is the only phase of ice for which the hydrogen-disordered counterpart has not been discovered yet. Using helium gas as a trick to stabilise ice II we now aim to finally prepare the so far illusive hydrogen-disordered counterpart of ice II and to solve one of the last remaining mysteries in the phase diagram of water. Applying pressure helps in the sense that the material can be heated to higher temperatures which makes the disordering more likely. We previously showed using gas-pressure cells that heating at 0.75 GPa does not lead to any disordering. To push the pressure range further, we now propose to use the Paris-Edinburgh cell which will drastically extend our pressure window. In addition to finding disordered ice II, we will also explore, for the first time, the upper pressure limit of He@ice II and we will find out to which as yet unknown high-pressure phase it will transform.