  Water's phase diagram displays enormous complexity with currently 17
experimentally-confirmed polymorphs of ice and several more predicted
computationally. For almost 120 years, it has been a stomping ground for
scientific discovery and ice research has often been a trailblazer for
investigations into a wide range of materials-related phenomena. Here, the
experimental progress of the last couple of years is reviewed, and open
questions as well as future challenges are discussed. The specific topics
include the polytypism and stacking disorder of ice I, the mechanism of the
pressure amorphization of ice I, the emptying of gas-filled clathrate hydrates
to give new low-density ice polymorphs, the effects of acid / base doping on
hydrogen-ordering phase transitions as well as the formation of solids
solutions between salts and the ice polymorphs, and the effect this has on the
appearance of the phase diagram. In addition to continuing efforts to push the
boundaries in terms of the extremes of pressure and temperature, the
exploration of the 'chemical' dimensions of ice research appears to now be a
newly emerging trend. It is without question that ice research has entered a
very exciting era.
