High-pressure transitions in methane hydrate

Three recent studies of the high-pressure transformations of methane hydrate [Chem. Phys. Lett, 325 (2000) 490; Proc. Natl. Acad. Sci. 97 (2000) 13484; Nature 410 (2001) 661] have reported apparently different behaviours. Detailed comparison of our X-ray and neutron diffraction data with those obtained in earlier work shows that there is in fact consistent behaviour on isothermal compression at room temperature with a transition from the clathrate I structure hydrate to a hexagonal hydrate with an unknown structure at similar to0.9 GPa. (C) 2001 Published by Elsevier Science B.V.