There has been a long controversy regarding the glass transition in low-density amorphous ice (LDA). The central question is whether or not it transforms to an ultraviscous liquid state above 136 K at ambient pressure prior to crystallization. Currently, the most widespread interpretation of the experimental findings is in terms of a transformation to a superstrong liquid above 136 K. In the last decade some work has also been devoted to the study of the glass transition in high-density amorphous ice (HDA) which is in the focus of the present review. At ambient pressure HDA is metastable against both ice I and LDA, whereas at > 0.2 GPa HDA is no longer metastable against LDA, but merely against high-pressure forms of crystalline ice. The first experimental observation interpreted as the glass transition of HDA was made using in situ methods by Mishima, who reported a glass transition temperature Tg of 160 K at 0.40 GPa. Soon thereafter Andersson and Inaba reported a much lower glass transition temperature of 122 K at 1.0 GPa. Based on the pressure dependence of HDA's Tg measured in Innsbruck, we suggest that they were in fact probing the distinct glass transition of very high-density amorphous ice (VHDA). Very recently the glass transition in HDA was also observed at ambient pressure at 116 K. That is, LDA and HDA show two distinct glass transitions, clearly separated by about 20 K at ambient pressure. In summary, this suggests that three glass transition lines can be defined in the p-T plane for LDA, HDA, and VHDA.

中文翻译：

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高密度非晶冰中的玻璃化转变。

关于低密度非晶冰（LDA）的玻璃化转变一直存在争议。核心问题是它在结晶之前是否在环境压力下在 136 K 以上转变为超粘液态。目前，对实验结果最广泛的解释是在 136 K 以上转变为超强液体。在过去的十年中，一些工作也致力于研究高密度非晶冰 (HDA) 的玻璃化转变这是本次审查的重点。在环境压力下，HDA 对冰 I 和 LDA 均具有亚稳态，而在 > 0.2 GPa 时，HDA 不再对 LDA 具有亚稳态，而仅对高压形式的结晶冰具有亚稳态。Mishima 使用原位方法进行了第一个解释为 HDA 玻璃化转变的实验观察，他报道了 0.40 GPa 下的玻璃化转变温度 Tg 为 160 K。此后不久，Andersson 和 Inaba 报道了在 1.0 GPa 下玻璃化转变温度低得多，为 122 K。根据在因斯布鲁克测量的 HDA Tg 的压力依赖性，我们认为他们实际上是在探索极高密度非晶冰 (VHDA) 的独特玻璃化转变。最近，在 116 K 的环境压力下也观察到了 HDA 的玻璃化转变。也就是说，LDA 和 HDA 显示出两种不同的玻璃化转变，在环境压力下明显分开约 20 K。总之，这表明可以在 pT 平面中为 LDA、HDA 和 VHDA 定义三个玻璃化转变线。