The crystal structure of $^{7}$Li$_{2}$ND

Recently much attention has been given to reversible hydrogen storage materials possessing high gravimetric capacity. Lithium amide/imide systems are promising candidates. Chen \textit{et al.}[1] found that a mixture of lithium amide and lithium hydride can reversibly store hydrogen up to 6.5 mass{\%} forming lithium imide (Li$_{2}$NH). Among them, the crystal structure of Li$_{2}$NH is still controversial. Balogh \textit{et al.}[2] have reported a cubic structure model. However, this model differs significantly from theoretical structure models. In this work, the crystal structure of the isotopically substituted $^{7}$Li$_{2}$ND has been investigated by powder neutron and synchrotron X-ray diffraction experiments. In our data some peaks, which should be a single peak for cubic symmetry, were obviously split indicating a lower symmetry than cubic for lithium imide. The structure of $^{7}$Li$_{2}$ND will be described. [1] P. Chen \textit{et al}., J. Phys. Chem. B \textbf{107} (2003) 10967. [2] M.P. Balogh \textit{et al.}, J. Alloys Compd. \textbf{420} (2006) 326.