Clarifying the role of acid and base dopants in the hydrogen-ordering phase transitions of ice

Using ISIS facilities, our team has discovered three new phases of ice: ices XIII, XIV and XV. These phases form in the presence of small amounts of hydrochloric acid. Yet, the role the acid dopant plays is still very poorly understood. In particular since the preparation of ice XI from the ‘ordinary’ ice I requires base doping and acid doping is ineffective. Now, we have found using calorimetry and X-ray diffraction that ice XIII can also be prepared with lithium hydroxide doping. Since this is the first case where acid and base doping are effective, we now have the perfect system for finally clarifying the role of the dopants. In addition to complementary DFT calculations, the experimental key question is now if acid and base dopants facilitate the same structural pathways leading towards the same ice XIII end-state. This question can only be answered with neutron diffraction.

我们团队借助ISIS装置发现了三种新型冰相：冰XIII、冰XIV与冰XV。此类冰相可在少量盐酸存在的条件下形成。然而，目前人们对酸掺杂剂所发挥的作用仍知之甚少。尤其值得注意的是，从「普通」冰I制备冰XI需采用碱掺杂，而酸掺杂对此过程并无效果。如今，我们通过量热法与X射线衍射实验发现，也可通过氢氧化锂掺杂制备冰XIII。由于这是首例酸碱掺杂均有效的案例，我们如今拥有了可最终阐明掺杂剂作用的理想实验体系。除辅以密度泛函理论（DFT）计算外，当前实验层面的核心问题在于：酸碱掺杂是否会经由相同的结构路径，最终得到完全一致的冰XIII终态。该问题唯有通过中子衍射实验方能解答。