ICMCS Seminar - Ice Ice baby: the discovery of ice XXII

From amorphous ice clouds in the vacuum of space, to superionic ice in the hot, dense interiors of giant planets, water ice is one of the most abundant molecular solids in the Solar System. Despite being a simple molecule, H2O possesses a complex pressure-temperature phase diagram, with 21 distinct crystalline phases reported to date.  

Upon room-temperature compression, only three known solid phases occur: ices VI, VII and X. In ice X (above ~60 GPa, or 600,000 atmospheres of pressure), hydrogen atoms sit midway between nearest-neighbour oxygen atoms, and the distinction between individual H2O molecules breaks down. At still higher pressures, computational work has long predicted that ice X should distort to form a new phase of orthorhombic ice. Experimental verification has, however, remained elusive for over 30 years.

In this seminar, I will present recent work from within ICMCS, where we observe the formation of post-ice-X phases at pressures over 300 GPa (3 million atmospheres).  Through diamond anvil cell experiments combined with synchrotron X-ray diffraction, Raman spectroscopy and infrared absorption measurements, we investigated the phase diagram of ice at 300 K beyond ice X. I will present our latest discovery of ice XXII and show how it matches long-standing predictions. These results reveal how hydrogen-bonded matter at pressures reaching those of ice-giant interiors.

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