Winkel Katrin, Elsaesser Michael S, Mayer Erwin, Loerting Thomas
Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, AustriaInstitute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
J Chem Phys. 2008 Jan 28;128(4):044510. doi: 10.1063/1.2830029.
An understanding of water's anomalies is closely linked to an understanding of the phase diagram of water's metastable noncrystalline states. Despite the considerable effort, such an understanding has remained elusive and many puzzles regarding phase transitions in supercooled liquid water and their possible amorphous proxies at low temperatures remain. Here, decompression of very high density amorphous ice (VHDA) from 1.1 to 0.02 GPa at 140 K is studied by means of dilatometry and powder x-ray diffraction of quench-recovered states. It is shown that the three amorphous states of ice are reversibly connected to each other, i.e., LDA<-->e-HDA<-->VHDA. However, while the downstroke VHDA-->e-HDA transition takes place in the pressure range of 0.06 GPa<p<0.40 GPa, the e-HDA-->LDA transition takes place quasi-discontinuously at p approximately 0.06 GPa. That is, two amorphous-amorphous transitions of a distinct nature are observed for the first time in a one-component system-a first-order-like transition (e-HDA-->LDA) and a transition which is not first-order like but possibly of higher order (VHDA-->e-HDA). VHDA and e-HDA are established as the most stable and limiting states in the course of the transition. We interpret this as evidence disfavoring the hypothesis of multiple first-order liquid-liquid transitions (and the option of a third critical point), but favoring a single first-order liquid-liquid transition (and the option of a second critical point).
对水的异常现象的理解与对水的亚稳态非晶态相图的理解密切相关。尽管付出了巨大努力，但这种理解仍然难以捉摸，关于过冷液态水的相变及其在低温下可能的非晶态替代物仍存在许多谜题。在此，通过对淬火恢复态的膨胀测量和粉末X射线衍射，研究了在140 K下将非常高密度非晶冰（VHDA）从1.1 GPa减压至0.02 GPa的过程。结果表明，冰的三种非晶态相互之间可逆连接，即LDA<-->e - HDA<-->VHDA。然而，虽然下行过程中VHDA-->e - HDA转变发生在0.06 GPa < p < 0.40 GPa的压力范围内，但e - HDA-->LDA转变在p约为0.06 GPa时准连续发生。也就是说，在单组分系统中首次观察到两种性质不同的非晶 - 非晶转变——一种类似一级的转变（e - HDA-->LDA）和一种非一级但可能是更高阶的转变（VHDA-->e - HDA）。VHDA和e - HDA在转变过程中被确定为最稳定和极限状态。我们将此解释为不利于多重一级液 - 液转变假设（以及第三个临界点的可能性）的证据，但有利于单一一级液 - 液转变（以及第二个临界点的可能性）。
