Dehydrogenation reaction of Li–Mg–N–H systems studied by in situ synchrotron powder X-ray diffraction and powder neutron diffraction

The dehydrogenation reaction of Mg(NH2)2 and LiH in a ratio of three to eight was investigated during heating in vacuum. Samples were prepared by two different routes. In situ synchrotron powder X-ray diffraction patterns indicated that an intermediate Li–Mg–N–H phase began to develop with consuming the starting materials around 150 °C and completed around 200 °C. A corresponding Li–Mg–N–D sample was prepared by heat treatment at 200 °C in vacuum for 8 h. The Rietveld refinement of both powder neutron and X-ray diffraction data provided reasonable fit with a primitive cubic structure with a composition Li2.6MgN2D1.4 and lattice dimension a = 5.0245(2) Å, smaller than corresponding values for stoichiometric imides. This is a kind of ‘Li-rich and H-poor’ imide, which is characteristic of imides by dehydrogenation under LiH-rich conditions.