Accurate and precise lattice parameters for D₂O and H₂O varieties of hexagonal ice (ice Ih, space group P6₃/mmc) have been obtained in the range 1.6 to 270 K. Precision of the lattice parameters (∼0.0002% in a and 0.0004% in c for D₂O, 0.0008% in a and 0.0015% in c for H₂O) is ensured by use of the time‐of‐flight method on one of the longest primary neutron flight‐path instruments in the world, the High‐Resolution Powder Diffractometer at the ISIS neutron source. These data provide a more precise description of the negative thermal expansion of the material at low temperatures than the previous synchrotron `gold standard' [Röttger et al. (1994). Acta Cryst. B50, 644–648], including the region below 10 K where the lattice parameters saturate. The volume expansivity of both isotopologues turns negative below 59–60 K, in excellent agreement with a recent dilatometry study. The axial expansivities are highly isotropic (differing by < 1% in D<sub>2</sub>O ice Ih). Furthermore, the c/a ratio of different D<sub>2</sub>O ice samples exhibit a statistically significant dispersion of ∼0.015% below 150 K that appears to depend on the thermal history of the sample, which disappears on warming above 150 K. Similarly, H<sub>2</sub>O ice exhibits a `kink' in the c/a ratio at ∼115 K. The most plausible explanation is a freezing‐in of the molecular reorientation process on cooling and subsequent relaxation on warming.

中文翻译：

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根据高分辨率的飞行时间中子粉末衍射数据，H2O和D2O冰Ih的精确和精确晶格参数介于1.6和270 K之间。

已获得D ₂ O和H ₂ O六方冰变种（冰I h，空间群P 6 ₃ / mmc）的精确且精确的晶格参数，范围为1.6至270K。晶格参数的精度（〜0.0002％）在一个在和0.0004％ç为d ₂ O，0.0008％在一个和0.0015％在c ^用于h ₂在世界上最长的一次中子飞行路径仪器之一——ISIS中子源上的高分辨率粉末衍射仪上-使用飞行时间方法来确保O）。这些数据比以前的同步加速器“金标准” [Röttger等人]更准确地描述了材料在低温下的负热膨胀。（1994）。Acta Cryst。乙50，644-648]，包括低于10 K，其中晶格参数饱和的区域。在最近的膨胀学研究中，两个同位素分子的体积膨胀率在59-60 K以下变为负值。轴向膨胀系数是高度各向同性的（在D ₂ O ice I h中相差<1％）。此外，Ç /一个不同的d比₂ ö冰样品表现出低于150ķ~0.015％，似乎取决于样品的热历史，它消失上高于150 K.类似地，H升温统计学显著分散₂ ö冰展品c / a比值在约115 K时出现“扭结” 。最合理的解释是在冷却时冻结了分子的重新定向过程，在加热后又放松了。