Loerting Thomas, Schustereder Werner, Winkel Katrin, Salzmann Christoph G, Kohl Ingrid, Mayer Erwin
Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria.
Phys Rev Lett. 2006 Jan 20;96(2):025702. doi: 10.1103/PhysRevLett.96.025702. Epub 2006 Jan 18.
On compressing low-density amorphous ice (LDA) at 125 K up to 1.6 GPa, two distinct density steps accompanied by heat evolution are observable in pressure-density curves. Samples recovered to 77 K and 1 bar after the first and second steps show the x-ray diffraction pattern of high-density amorphous ice (HDA) and very HDA (VHDA), respectively. The compression of the once formed HDA takes place linearly in density up to 0.95 GPa, where nonlinear densification and HDA --> VHDA conversion is initiated. This implies a stepwise formation process LDA--> HDA --> VHDA at 125 K, which is to the best of our knowledge the first observation of a stepwise amorphous-amorphous-amorphous transformation sequence. We infer that the relation of HDA and VHDA is very similar to the relation between LDA and HDA except for a higher activation barrier between the former. We discuss the two options of thermodynamic versus kinetic origin of the phenomenon.
在125 K下将低密度非晶冰（LDA）压缩至1.6 GPa时，在压力-密度曲线上可观察到两个明显的密度台阶并伴有热释放。在第一步和第二步之后恢复到77 K和1巴的样品分别显示出高密度非晶冰（HDA）和极高密度非晶冰（VHDA）的X射线衍射图案。一旦形成的HDA在密度上线性压缩至0.95 GPa，此时开始非线性致密化以及HDA向VHDA的转变。这意味着在125 K下LDA→HDA→VHDA的逐步形成过程，据我们所知，这是首次观察到的非晶-非晶-非晶逐步转变序列。我们推断，除了前者之间具有更高的活化能垒外，HDA和VHDA的关系与LDA和HDA之间的关系非常相似。我们讨论了该现象的热力学起源与动力学起源这两种情况。
