Three years ago, chemists found evidence for the existence of a new variety of ice. Until then, 18 types of crystalline ice were known. The team now reports on the elucidation of the crystal structure of ice XIX using neutron diffraction.
For the clarification of the crystal structure, an essential technical hurdle had to be overcome. In an investigation using neutron diffraction, it is necessary to replace the light hydrogen in water with deuterium (“heavy hydrogen”). “”Unfortunately, this also changes the time scales for ordering in the ice manufacturing process,” says Loerting. “But Ph.D. student Tobias Gasser then had the crucial idea of adding a few percent of normal water to the heavy water — which turned out to speed up the ordering immensely.” With the ice obtained in this way, the Innsbruck scientists were finally able to measure neutron data on the high-resolution HRPD instrument at the Rutherford Appleton Laboratory in England and painstakingly solve the crystal structure of ice XIX. This required finding the best crystal structure out of several thousand candidates from the measured data — much like searching for a needle in a haystack. A Japanese research group confirmed the Innsbruck result in another experiment under different pressure conditions. Both papers have now been published jointly in Nature Communications.
Six ice forms discovered in Innsbruck
While conventional ice and snow are abundant on Earth, no other forms are found on the surface of our planet — except in research laboratories. However, the high-pressure forms ice VI and ice VII are found as inclusions in diamonds and have therefore been added to the list of minerals by the International Mineralogical Association (IMA). Many varieties of water ice are formed in the vastness of space under special pressure and temperature conditions. They are found, for example, on celestial bodies such as Jupiter’s moon Ganymede, which is covered by layers of different ice varieties.
Ice XV and ice XIX represents the first sibling pair in ice physics in which the oxygen lattice is the same, but the pattern how hydrogen atoms are ordered is different. “”This also means that for the first time it will now be possible to realize the transition between two ordered ice forms in experiments,” Thomas Loerting is pleased to report. Since the 1980s, researchers at the University of Innsbruck, Austria, are now responsible for the discovery of four crystalline as well as two amorphous ice forms.
The current research work was carried out within the framework of the Research Platform for Materials and Nanoscience at the University of Innsbruck and was financially supported by the Austrian Science Fund FWF.