Issue |
Europhys. Lett.
Volume 34, Number 9, June III 1996
|
|
---|---|---|
Page(s) | 675 - 680 | |
Section | Condensed matter: structure, thermal and mechanical properties | |
DOI | https://doi.org/10.1209/epl/i1996-00514-3 | |
Published online | 01 September 2002 |
Inelastic incoherent neutron scattering study of the pressure dependence of ice VII and VIII
1
Department of Physics, University of Salford - Salford, M5 4WT, UK
2
Rutherford-Appleton Laboratory - Chilton, Didcot, OXON, OX11, 0QX, UK
Incoherent inelastic neutron-scattering spectra of ice VII and VIII have
been obtained at an in situ pressure of on the TFXA
spectrometer at the pulsed neutron source, ISIS. Comparisons with recovered phases (at
ambient pressure) show large shifts of the phonon modes. For instance, the optic peak for
ice VIII is shifted from 25 to 32 meV (
). The coefficient
of increase of the frequency of the mode with pressure,
, is 2.3 meV/GPa
(or
). In ice VII, the
proton-disordered form of ice VIII, the spectra, measured under the same pressure,
show that: firstly, the sharp features of the librational band in the region 50–100
meV disappear, indicating that the protons are indeed disordered as is found in other
proton-disordered forms of ice; secondly, a weak higher-energy optic mode at 49.5
meV appears due to the presence of the second proton configuration as seen in other
proton-disordered ice Ic.
PACS: 61.12.-q – Neutron diffraction and scattering / 63.20.-e – Phonons and vibrations in crystal lattices
© EDP Sciences, 1996
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