NEUTRON-DIFFRACTION STUDY OF THE STRUCTURE OF DEUTERATED ICE-VIII TO 10 GPA

The pressure dependence of the structure of deuterated ice VIII has been studied by time-of-flight neutron powder diffraction up to 10 GPa. The precision of the values of the intramolecular bond length O-D is +/- 0.003 angstrom or better at all pressures, and the rate of increase of the O-D bond length is found to be 0.0004(4) angstrom GPa-1. This value is significantly smaller than previous estimates, which all incorporate the assumption that the form of the O-H potential is constant with pressure. It appears that this is not the case.