Amongst the more than 18 different forms of water ice, only the common hexagonal phase and the cubic phase are present in nature on Earth. Nonetheless, it is now widely recognized that all samples of ‘cubic ice’ discovered so far do not have a fully cubic crystal structure but instead are stacking-disordered forms of ice I (namely, ice Isd), which contain both hexagonal and cubic stacking sequences of hydrogen-bonded water molecules. Here, we describe a method to obtain large quantities of cubic ice Ic with high structural purity. Cubic ice Ic is formed by heating a powder of D₂O ice XVII obtained from annealing of pristine C₀ hydrate samples under dynamic vacuum. Neutron diffraction experiments performed on two different instruments and Raman spectroscopy measurements confirm the structural purity of the cubic ice, Ic. These findings contribute to a better understanding of ice I polymorphism and the existence of the two natural ice forms.

在超过 18 种不同形式的水冰中，只有常见的六方相和立方相存在于地球的自然界中。尽管如此，现在人们普遍认为，迄今为止发现的所有“立方冰”样本都没有完全立方晶体结构，而是堆积无序形式的冰 I（即冰 Isd），其中包含六边形和立方堆积氢键水分子序列。在这里，我们描述了一种获得大量具有高结构纯度的立方冰 Ic 的方法。立方冰 Ic 是通过加热从原始 C _{0退火获得的 D 2 O ice XVII 粉末形成的}在动态真空下水合样品。在两种不同仪器上进行的中子衍射实验和拉曼光谱测量证实了立方冰的结构纯度 Ic。这些发现有助于更好地理解冰 I 多态性和两种天然冰形式的存在。