Structures of solid deuterium bromide and deuterium iodide

The crystal structures of the three solid phases of deuterium bromide and deuterium iodide have been determined using the neutron powder diffraction profile structure refinement technique. Except for phase III of deuterium iodide, which has 32 molecules per unit cell, all other phases (I, II & III of DBr and I & II of DI) have four molecules per unit cell. Phase I, for both DBr and DI, has a structure which is face-centered cubic, space group O5h - Fm3m with 12-fold disordered positions for the deuterium.

Both DBr and DI in phase II have 2 disordered molecular orientations which give on average a centrosymmetric base-centered orthorhombic structure, space group D182h - Cmca. The phase III structure of DBr, as determined from profiles taken at 12K and 85K, is an ordered structure composed of deuterium bonded zig-zag chains. The space group is C122v - Cmc21 which is non-centrosymmetric base-centered orthorhombic.

For DI, phase III has a structure which is face-centered orthorhombic, space group C192v - Fdd2 as determined from a profile taken at 15K. Actually, at this temperature, the sample was a mixture of phase II and phase III.