Structural Mechanisms of Phase Transitions of Water Ices II, IV, and V to Metastable Ice Ic at Atmospheric Pressure

Model structural mechanisms of transitions between crystalline water ices II → Ic, IV → Ic, and V → Ic are proposed. It is established that in the proposed II → Ic transition mechanism, one of the three systems of infinite parallel chains consisting of adjacent hexacycles and running along the 〈0001〉 direction of ice II is preserved, and these chains become parallel to one of the 〈211〉 directions of ice Ic. The proposed mechanism of the V → Ic transition preserves both systems of infinite parallel chains of adjacent hexacycles extended along the [101] and [10–1] directions of ice V; in ice Ic, they run along two directions 〈211〉 parallel to the same {120} plane. According to the proposed mechanism of the IV → Ic transition, puckered surfaces of hexacycles are retained. In all three cases, 3/4 of all hydrogen bonds are retained during the transition, and 1/4 of the bonds are rearranged. It is shown that the structures of ices II, IV, and V consist of the same structural element, which is slightly modified in ice V.