The pressure dependence of the structure of deuterated ice VIII has be
en 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 inco
rporate the assumption that the form of the O-H potential is constant
with pressure. It appears that this is not the case.