Fig. 1: Phase diagram of hydrogen hydrate and ice with experimental paths in this study.
From: Ice Ic without stacking disorder by evacuating hydrogen from hydrogen hydrate
Phase boundaries for hydrogen hydrates and ices are drawn using thick blue lines and thin black lines, respectively. Experimental p-T paths are shown as black arrows in alphabetical sequence from a to g. The structural models for a high-pressure form of hydrogen hydrate, C2, and ice Ic are schematically drawn with a newly found amorphous-like state as an intermediate transitional state from C2 to ice Ic. Red, white, and light blue balls in the structure model depict oxygen, hydrogen in water molecules, and hydrogen in guest molecules, respectively. Note that hydrogens in water molecules are disordered, so that two of four possible sites surrounding one oxygen are actually occupied.
