International Conference on Gas Hydrates (ICGH) (6th : 2008)

A LOW SYMMETRY FORM OF STRUCTURE H CLATHRATE HYDRATE Ripmeester, John A.; Ratcliffe, Christopher I.; Udachin, Konstantin A.


In this paper we report a low symmetry version of structure H hydrate that results from the hexagonal form on cooling below 167 K. Phase changes with temperature in the common clathrate hydrates structural families I, II and H have not been observed before, except in doped systems where ordering transitions take place or in the structure I hydrate of trimethylene oxide where the guest molecule dipoles are known to order. Since there is an inverse relationship between the effect of temperature and pressure on ices, it may well be that the low symmetry form reported at low temperature can also be reached by applying high pressure, and that in fact some of the observed high pressure phases are lower symmetry versions of hexagonal sH.

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