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 {} or better at all pressures, and the rate of increase of the O-D bond length is found to be 0.0004(4) {} 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.