Crystal structures and phase transformation of deuterated lithium imide, Li2ND

We have investigated the crystal structure of deuterated lithium imide, Li2ND, by means of neutron and X-ray diffraction. An order disorder transition occurs near 360 K. Below that temperature Li2ND can be described to the same level of accuracy as a disordered cubic (Fd3m) structure with partially occupied Li 32e sites or as a fully occupied orthorhombic (Imal or Imtril) structure. The high temperature phase is best characterized as disordered cubic (Fm3m) with D atoms randomized over the 1921 sites. Density functional theory calculations complement and support the diffraction analyses. We compare our findings in detail with previous studies.