Neutron-scattering studies of the phase transitions in high-pressure ices during annealing

Inelastic incoherent neutron scattering was used to study the phase transition process of high-density amorphous (HDA) ice to low-density amorphous (LDA) ice by thermal treatment. The results show that when the annealing temperature is lower than 136 K no obvious phase-transition is observed, and transformation of the HDA ice to the LDA ice occurs between 136 and 144 K. From comparison of the measured inelastic neutron-scattering spectra for HDA ice and ice Ih, it is found that the internal interactions (covalent bond O-H and three-body interaction H-O-H) are stronger in HDA ice, which correlates with the longer nearest O-O distances in HDA ice compared to ice Ih (2.80 and 2.75 Å, respectively). The report also discusses the differences in vibrational spectra of LDA ices obtained by different methods (annealing HDA ice and depositing water vapour on a cold substrate).