Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 33: Molecular Structure
CPP 33.3: Vortrag
Donnerstag, 28. Februar 2008, 15:30–15:45, C 230
"Phase"-Transitions in Amorphous Water — •Katrin Winkel1, Michael S. Elsaesser2, Erwin Mayer1, and Thomas Loerting1,2 — 1Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck — 2Institute of Physical Chemistry, University of Innsbruck
An understanding of the anomalies of water is closely linked to an understanding of the phase diagram of the metastable non-crystalline states of ice. Three distinct structural states of amorphous water are known, they are called low- (LDA), high- (HDA) and very high density amorphous ice (VHDA). In our present work decompression of VHDA from 1.1 GPa 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. However, while the downstroke VHDA-->e-HDA transition is apparently continuous, the e-HDA-->LDA transition takes place quasi-discontinuously. 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 our results as evidence disfavouring the hypothesis of multiple first-order liquid-liquid transitions (and the option of a third critical point), but favouring a single first-order liquid-liquid transition (and the option of a second critical point).