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.

冰V（Ice V）是水冰的无序单斜晶型，具有复杂的结构拓扑特征。在针对于液氮温度下恢复至常压的冰V的研究中，我们观测到了结构弛豫现象，我们认为该现象源于水分子取向有序性的改变。为验证这一假说，我们计划利用高分辨中子粉末衍射（high-resolution neutron powder diffraction）技术，采集未弛豫态与弛豫态的D₂O冰V的高质量结构数据集。我们此前的研究还表明，冰V沿其c轴呈现线性负膨胀特性，我们认为该特性与同位素取代引发的异常晶格膨胀相关。鉴于通过计算手段预测此类同位素效应极具挑战性，对上述相关性开展实验验证至关重要，因此我们还计划采集H₂O冰V的高分辨衍射数据。