Overview of the recent studies on high‐pressure impurity ices

Abstract In the present short review, we briefly overview the history of ice polymorphism under high‐pressure and the recent progress on impurity ices (clathrate ice, salty ice, doped ice, empty ice, etc.), including our contributions due form high‐pressure Raman investigations to these research fields. In particular, the unique roles of impurities in ice, which are (1) acceleration of proton ordering at lower temperatures, (2) offering a clue to form new ice phases, and (3) phase transitions other than the original equilibrium stability region of pure H 2 O, ice are introduced. Then, as prospects, we address promising impacts on a new area of ice physics with the active use of impurities.