Anomalies and phase transitions of dense ice

Details Anomalies and phase transitions of dense ice Anomalies and phase transitions of dense ice

Oct 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011epsc.conf..756c&link_type=abstract

EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. http://meetings.copernicus.org/epsc-dps2011, p.756

Physics

Scientific paper

We propose that the anomalies in ice VII and ice VIII can be explained by the formation of ferroelectric (FE) and anti-ferroelectric (AFE) domains. In the FE domains the dipoles point along the same direction along the 4-fold axis, while in AFE they point alternatively up and down. The splitting of the X-ray diffraction peaks and the appearance of new Raman modes are the result of different a/c ratios in the two FE and AFE parts of the structure [2,3]. Then, based on lattice dynamical calculations, we show that the transition between ices VII and VIII and ice X goes through a disordered phase X in the 60- 115 GPa pressure range. In this regime the H atoms are allowed to freely bounce back and forth between their two O neighbors. Ice X is stable up to about 420 GPa. The first post-ice-X structure occurs due to a phonon softening in ice X. The resulting structure has orthorhombic symmetry [4,5,6]. We show that the softening is also visible in the development of an elastic anomaly after 160 GPa.

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