Ice XIV (Ice-fourteen)
Ice-fourteen (ice XIV) is the proton-ordered form of ice-twelve, formed by doping with 0.01 M HCl (as DCl with D2O) below 118 K and at 1.2 GPa to facilitate the phase transition . The transformation is reversible with temperature change, but less proton-ordering of ice-fourteen is found at lower pressure . The crystals were orthorhombic P212121 with cell
dimensions a 8.350 Å, b 8.139 Å and c 4.083 Å (90°,
90°, 90°, 12 molecules; at atmospheric pressure
and 80 K) and a unit cell contains 12 water molecules . 8 out of the 24 proton positions in the unit cell (as some labeled * opposite forming chains; the shown ordering of these is predominant) remained mostly disordered. It is possible that two further metastable proton ordered forms of ice XIV may form under kinetically controlled conditions, as shown by simulations .
Interactive Jmol structures are given.