抄録
The structural pressure dependence of the high-pressure ices VII and VIII has been measured up to 20 GPa by neutron powder diffraction. Measurements of the atomic thermal motion reveal that, while it is strongly reduced by pressure in both phases, the stepwise change in the oxygen thermal motion at the VIII/VII transition is pressure independent within the precision of the measurements. Also, the O-D bondlength in ice VIII changes by less 0. 002 Å to 20 GPa. These results suggest that the site-separation of the disordered oxygen atoms in ice VII and the direction of the disorder displacement remain closely similar to those found at 5 GPa.
