Absence of amorphous forms when ice is compressed at low temperature
Absence of amorphous forms when ice is compressed at low temperature
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DOI：
10.1038/s41586-019-1204-5
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发表时间：
2019-05
期刊：
影响因子：
64.8
通讯作者：
C. Tulk;J. Molaison;A. Makhluf;C. Manning;D. Klug
中科院分区：
文献类型：
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作者：
C. Tulk;J. Molaison;A. Makhluf;C. Manning;D. Klug
无定形水冰至少有三种不同的结构形式，它们都缺乏长程晶体有序性。高密度无定形冰（HDA）最初是通过在低于130开尔文的温度下将冰压缩到11毫巴而产生的，这个过程被描述为热力学熔化，这意味着HDA是一种玻璃态的水。这个概念，以及将HDA可逆地转化为低密度无定形冰的能力，启发了双液态水模型，该模型将无定形相与深度过冷状态（低于228开尔文）的两种液态沃茨联系起来，以解释水的许多异常（如密度和热容异常）。然而，HDA的形成也被归因于机械不稳定性，导致结构坍塌，并与动力学太慢而不能发生再结晶有关。这种解释是支持模拟，类比结构相似的系统，并观察晶格振动软化冰被压缩，。这也与最近观察到的冰在更高温度下的压缩相一致-在这里，我们进一步探讨了动力学的作用，并表明，如果缓慢进行，即使在100开尔文（HDA通常形成的区域），冰I的压缩也会产生质子有序但非互穿的冰IX′，然后是质子有序和互穿的冰XV′，最后是冰VIII′。相比之下，快速压缩产生HDA，但没有冰IX，冰I直接转化为冰XV′在结构上受到抑制。这些观测结果表明，HDA的形成是低密度冰I和高密度冰XV′之间动力学停滞转化的结果，并挑战了将无定形冰与过冷液态水联系起来的理论。
Amorphous water ice comes in at least three distinct structural forms, all lacking long-range crystalline order. High-density amorphous ice (HDA) was first produced by compressing ice I to 11 kilobar at temperatures below 130 kelvin, and the process was described as thermodynamic melting, implying that HDA is a glassy state of water. This concept, and the ability to transform HDA reversibly into low-density amorphous ice, inspired the two-liquid water model, which relates the amorphous phases to two liquid waters in the deeply supercooled regime (below 228 kelvin) to explain many of the anomalies of water (such as density and heat capacity anomalies). However, HDA formation has also been ascribed to a mechanical instability causing structural collapse and associated with kinetics too sluggish for recrystallization to occur. This interpretation is supported by simulations, analogy with a structurally similar system, and the observation of lattice-vibration softening as ice is compressed,. It also agrees with recent observations of ice compression at higher temperatures—in the ‘no man’s land’ regime, between 145 and 200 kelvin, where kinetics are faster—resulting in crystalline phases,. Here we further probe the role of kinetics and show that, if carried out slowly, compression of ice I even at 100 kelvin (a region in which HDA typically forms) gives proton-ordered, but non-interpenetrating, ice IX′, then proton-ordered and interpenetrating ice XV′, and finally ice VIII′. By contrast, fast compression yields HDA but no ice IX, and direct transformation of ice I to ice XV′ is structurally inhibited. These observations suggest that HDA formation is a consequence of a kinetically arrested transformation between low-density ice I and high-density ice XV′ and challenge theories that connect amorphous ice to supercooled liquid water.