Thermally Induced Phase Transition of Cubic Structure II Hydrate: Crystal Structures of Tetrahydropyran-CO2 Binary Hydrate

Satoshi Takeya, Hiroshi Fujihisa, Saman Alavi, Ryo Ohmura

Research output: Contribution to journalArticlepeer-review

Abstract

We report a thermally induced phase transition of cubic structure II hydrates of tetrahydropyran (THP) and CO2 below about 140 K. The phase transition was characterized by powder X-ray diffraction measurements at variable temperatures. A dynamical ordering of the CO2 guests in small pentagonal dodecahedral 512 host water cages, not previously observed in the simple CO2 hydrate, occurs simultaneously with the symmetry lowering transition from a cubic structure II (space group Fd-3m with cell dimensions a = 17.3202(7) Å at 153 K) to a tetragonal (space group I41/amd with cell dimensions a = 17.484(4) Å and c = 12.145(1) Å at 138 K) unit cell. The effect of guest molecules on the phase transition at low temperatures is discussed, which demonstrates that the clathrate hydrate structures and thermodynamic properties can be modified by adjusting the size and chemical structure of larger and smaller guest molecules.

Original languageEnglish
Pages (from-to)1885-1891
Number of pages7
JournalJournal of Physical Chemistry Letters
Volume14
Issue number7
DOIs
Publication statusPublished - 2023 Feb 23

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry

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