title: Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form.
abstract: The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH4 ) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH4 hydrate, but not 1-propanol+CH4 hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2-propanol+CH4 hydrate can be explained by the restriction of the motion of 2-propanol within the 5(12) 6(4) host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, 305-8565, Ibaraki, Japan. s.takeya@aist.go.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takeya
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, 305-8565, Ibaraki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujihisa
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, 305-8565, Ibaraki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamawaki
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, 305-8565, Ibaraki, Japan.
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Gotoh
authors.affiliation: Keio University, 3-14-1 Hiyoshi, Kohoku-Ku, Yokohama, 223-8522, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Ohmura
authors.affiliation: National Research Council of Canada, 100 Sussex Dr., Ottawa, ON, K1A0R6, Canada.
authors.forename: Saman
authors.initials: S
authors.lastname: Alavi
authors.affiliation: National Research Council of Canada, 100 Sussex Dr., Ottawa, ON, K1A0R6, Canada.
authors.forename: John A
authors.initials: JA
authors.lastname: Ripmeester
keywords: clathrates; gas hydrates; inclusion compounds; phase transitions; powder X-ray diffraction