Water is highly important in chemistry, biology and geology, and is thought to be essential for the formation and evolution of life. H2O also shows immense structural complexity in its solid forms which was illustrated once more by our recent discovery of ice XV.
The first part of the talk will focus on hydrogen ordering phenomena in ice which lead to either ferroelectric or antiferroelectric ice structures. Various disorder to order phase transitions have been investigated in detail by using powder neutron diffraction, Raman spectroscopy and differential scanning calorimetry. The ordering properties of the various phases are compared, and the influence of point defects on the ordering transitions is discussed as well as the relative stabilities of the various phases. The ordered structures can be used as benchmarks for testing computer models of water. Interestingly, in the case of our most recent phase, ice XV, the experimental structure is in clear disagreement with the structure predicted by DFT calculations. The second part of the talk will be concerned with the relaxation and crystallisation processes observed upon isobaric heating of high-density amorphous ice.