Loerting Thomas, Salzmann Christoph G, Winkel Katrin, Mayer Erwin
Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
Phys Chem Chem Phys. 2006 Jun 28;8(24):2810-8. doi: 10.1039/b603159e. Epub 2006 May 18.
The exact nature of the relationship between high-density (HDA) and very-high-density (VHDA) amorphous ice is unknown at present. Here we review the relation between HDA and VHDA, concentrating on experimental aspects and discuss these with respect to the relation between low-density amorphous ice (LDA) and HDA. On compressing LDA at 125 K up to 1.5 GPa, two distinct density steps are observable in the pressure-density curves which correspond to the LDA --> HDA and HDA --> VHDA conversion. This stepwise formation process LDA --> HDA --> VHDA at 125 K is the first unambiguous observation of a stepwise amorphous-amorphous-amorphous transformation sequence. Density values of amorphous ice obtained in situ between 0.3 and 1.9 GPa on isobaric heating up to the temperatures of crystallization show a pronounced change of slope at ca. 0.8 GPa which could indicate formation of a distinct phase. We infer that the relation between HDA and VHDA is very similar to that between LDA and HDA except for a higher activation barrier between the former. We further discuss the two options of thermodynamic phase transition versus kinetic densification for the HDA --> VHDA conversion.
目前，高密度（HDA）和极高密度（VHDA）非晶冰之间关系的确切性质尚不清楚。在此，我们回顾HDA和VHDA之间的关系，重点关注实验方面，并结合低密度非晶冰（LDA）与HDA之间的关系进行讨论。在125 K下将LDA压缩至1.5 GPa时，在压力-密度曲线上可观察到两个明显的密度阶跃，它们分别对应于LDA→HDA和HDA→VHDA的转变。在125 K下LDA→HDA→VHDA的这种逐步形成过程是首次明确观察到的非晶-非晶-非晶转变序列。在等压加热至结晶温度的过程中，于0.3至1.9 GPa原位获得的非晶冰密度值在约0.8 GPa处显示出明显的斜率变化，这可能表明形成了一种独特的相。我们推断，HDA和VHDA之间的关系与LDA和HDA之间的关系非常相似，只是前者之间的活化能垒更高。我们还进一步讨论了HDA→VHDA转变的热力学相变与动力学致密化这两种情况。
