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Collapse of an ice clathrate under pressure observed via thermal conductivity measurements
Umeå University, Faculty of Science and Technology, Physics.
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, Vol. 78, 174201- p.Article in journal (Refereed) Published
Abstract [en]

Irreversible transformation of the tetrahydrofuran ice clathrate at 130 K was studied by measuring thermal conductivity k with increase in pressure p. Initially, k increases slowly with p up to 0.75 GPa where it levels off, is roughly constant up to 0.95 GPa, then decreases up to 1.05 GPa. Pressure collapses the clathrate structure, plausibly beginning with lattice distortion, and k increases at 1.05 GPa in a sharp sigmoid-shape manner due to large densification until the transformation is complete at 1.25 GPa. This is the opposite of that found for ice whose k decreases first slowly with increase in p and then rapidly in an inverted sigmoidshape manner [O. Andersson and H. Suga, Phys. Rev. B 65, 140201 (2002)]. At 1.08 GPa and 131 K, k increases with time t (s) according to exp(t /2945), which is also the opposite of the collapse of ice [G. P. Johari and O. Andersson, Phys. Rev. B 70, 184108 (2004)]. The difference in its behavior is attributed to strong phonon scattering from the tetrahydrofuran guest molecules. k of the collapsed clathrate is 30% less than that for the collapsed ice, which is comparable with the 25% lesser k of the tetrahydrofuran-water solution from k of water at ambient pressure. On depressurizing at 130 K, k decreases progressively more rapidly and k of the collapsed state at 0.3 GPa is slightly lower than that of the as-made clathrate, showing that its original structure is not recovered.

Place, publisher, year, edition, pages
2008. Vol. 78, 174201- p.
URN: urn:nbn:se:umu:diva-11299DOI: 10.1103/PhysRevB.78.174201OAI: diva2:150970
Available from: 2008-12-09 Created: 2008-12-09 Last updated: 2009-03-13Bibliographically approved

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