Ice β-XV – a novel ice polymorph

Water molecules can form different hydrogen-bonded networks, a property known as ice polymorphism. So far 18 different networks have been characterized using neutron diffraction on D2O samples. In our recent experiments we have discovered a novel ice polymorph, called ice β-XV (Gasser et al., Chem. Sci. 9 (2018)) 4224). It is a daughter polymorph to ice VI, and a sister polymorph to ice XV - it shares the same type of oxygen network with them. Refinement of its crystal structure has so far been hampered because an adverse isotope effect has hindered access to D2O ice β-XV. In our very recent work we found a route to the D2O form, allowing us to refine its crystal structure using the HRPD instrument. Upon heating ice β-XV experiences an order-to-order transition in its network of H atoms. This is the first of its kind known in ice physics and will be studied in detail on HRPD by us.

水分子可构筑多种不同的氢键网络，这一特性被称为冰的多态性（ice polymorphism）。迄今为止，研究人员已通过重水（D₂O）样品的中子衍射（neutron diffraction）技术表征了18种不同的氢键网络结构。在近期的实验中，我们发现了一种全新的冰相，将其命名为冰β-XV（Gasser等，《化学科学》（Chem. Sci.）9卷（2018年），第4224页）。该相是冰VI的子相，同时与冰XV互为姊妹相——三者共享完全一致的氧原子骨架网络。此前，由于不利的同位素效应阻碍了重水型冰β-XV的制备与获取，其晶体结构的精修（crystal structure refinement）工作长期受阻。在最新的研究中，我们成功开发出获取重水型冰β-XV的可行方法，得以借助HRPD衍射仪完成其晶体结构的精修工作。当对冰β-XV进行加热时，其氢原子网络会发生有序-有序相变（order-to-order transition）。这是冰物理学领域迄今已知的首例此类相变，我们将依托HRPD衍射仪对其开展深入的系统性研究。