Origin of the structural relaxation in ice V and the H/D volume isotope effect

Ice V is disordered monoclinic polymorph of water ice, with a complex structural topology. In our work on ice V (recovered to atmospheric pressure at liquid-nitrogen temperatures) we have observed a structural relaxation we believe is due to a change in the orientational order of the water molecules. To test this hypothesis, we propose to measure high-quality structural datasets from both the un-relaxed and the relaxed forms of D2O ice V using high-resolution neutron powder diffraction. Our earlier work also showed that ice V exhibits negative linear expansion along its c-axis, a property we believe to be correlated with anomalous lattice expansion due to isotopic substitution. Since these isotope effects have proven so challenging to predict computationally, experimental verification of these correlations are essential, and we propose also to measure high-resolution data from H2O ice V.