title: Nature of amorphous polymorphism of water.
abstract: We report elastic and inelastic neutron scattering experiments on different amorphous ice modifications. It is shown that an amorphous structure (HDA') indiscernible from the high-density phase (HDA), obtained by compression of crystalline ice, can be formed from the very high-density phase (vHDA) as an intermediate stage of the transition of vHDA into its low-density modification (LDA'). Both HDA and HDA' exhibit comparable small-angle scattering signals characterizing them as structures heterogeneous on a length scale of a few nanometers. The homogeneous structures are the initial and final transition stages vHDA and LDA', respectively. Despite their apparent structural identity on a local scale, HDA and HDA' differ in their transition kinetics explored by in situ experiments. The activation energy of the vHDA-to-LDA' transition is at least 20 kJ/mol higher than the activation energy of the HDA-to-LDA transition.
authors.affiliation: Institut Laue-Langevin, F-38042 Grenoble CEDEX, France.
authors.forename: M M
authors.initials: MM
authors.lastname: Koza
authors.forename: B
authors.initials: B
authors.lastname: Geil
authors.forename: K
authors.initials: K
authors.lastname: Winkel
authors.forename: C
authors.initials: C
authors.lastname: Köhler
authors.forename: F
authors.initials: F
authors.lastname: Czeschka
authors.forename: M
authors.initials: M
authors.lastname: Scheuermann
authors.forename: H
authors.initials: H
authors.lastname: Schober
authors.forename: T
authors.initials: T
authors.lastname: Hansen