Abstract
The crystal structure of the paraelectric and antiferroelectric phase (Tc = 246.1 K) of deuterated copper formate tetradeuterate was refined from neutron diffraction data. Final R factors were 0.022 and 0.033 respectively. Superstructure reflections in both phases indicate P1 as the correct space group. The refinement was carried out in the approximate space groups P21/a (296 K) and P21/n (120 K). The justification for this choice is discussed. The deuterium population parameters of the paraelectric phase are related to the hindered rotation of the water molecules. Accurate positional and thermal parameters for the antiferroelectric phase are presented and a value for the dipole moment was calculated from the refined ordering of the water layers.