Pressure-induced amorphization of clathrate hydrates

Compression and decompression of clathrate hydrates have been carried out in order to investigate the onset pressures above which the crystalline forms begin to collapse at OK and do not revert back to the original structures upon decompression. Several proton-disordered structures of clathrate hydrate I encapsulating noble gases were subjected to compression, the steepest descent minimization of potential energy, the subsequent expansion to the original volume, and the steepest descent minimization. It was found that above the onset pressure, depending on guest species, even the fully occupied hydrates are compressed inelastically, and transformed into amorphous forms from which crystalline structures are no longer recovered by decompression at 0 K.