High-density Ihda and low-density Ilda amorphous ice phases have been investigated by inelastic neutron scattering (INS) with emphasis on the energy window from 0.5 to 20 meV. At variance with earlier measurements the spectra in the Ihda phase show a simple ω2 behaviour in the acoustic region and the temperature dependence is found to be harmonic. Ihda converts with a strongly temperature-dependent rate towards Ilda ice. We have investigated in detail the time evolution of both the static and dynamic response functions at several temperatures. Elastic small-angle signals indicate the presence of strong heterogeneities at the early stages of the conversion process. At least two different time scales are present in the transition. The structural changes are reflected in the frequency distribution. The first peak in the phonon density-of-states softens appreciably when going from Ihda to Ilda. In the acoustic region there is evidence that Ilda is softer than both Ihda and crystalline cubic ice Ic. No signs of a fast ps process related to melting can be detected in the dynamics.
- Amorphous ice
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering