The incompressibility and thermal expansivity of D2O ice II determined by powder neutron diffraction

Abstract

Using high-resolution neutron powder diffraction, the molar volume of a pure sample of D2O ice II has been measured, within its stability field, at 225 K, over the pressure range 0.25 <P< 0.45 GPa. Ar gas was used as the pressure medium, to avoid the formation of `stuffed ice' gas hydrates encountered when using He. The third-order Birch–Murnaghan equation of state parameters of helium-free D2O ice II, referenced to 225 K, are:V0,225= 306.95 ± 0.04 Å3(1299.7 ± 0.2 kg m−3),K0,225= 12.13 ± 0.07 GPa, with K'_{0,225} fixed at 6.0. The thermal expansivity of metastable D2O ice II samples recovered to ambient pressure has also been measured, over the range 4.2 <T< 160 K; above 160 K an irreversible transition to ice Icwas observed. The volumetric expansion coefficient, αV, atP= 0 andT= 225 K, is predicted to be 2.48 × 10−4 K−1.