Neutron diffraction study of deuterium ordering in C15 type TaV2Dx (x>1) in the temperature range of 1.5-295 K

Neutron diffraction investigations on the C15-type Laves phase deuterides TaV2Dx with nominal compositions 1.3 less than or equal to x less than or equal to 1.65 have shown that at T>150 K deuterium atoms (D) occupy 969 sites of space group Fd (3) over bar m, i.e. tetrahedral interstices with [Ta2V2] coordination, However, the D positions are found to be considerably displaced from the geometrical centres of these sites. Below 150 K deuterium ordering is revealed by the appearance of superlattice peaks. Their intensities are found to increase substantially with increasing D content.