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 degrees C and completed around 200 degrees C. A corresponding Li-Mg-N-D sample was prepared by heat treatment at 200 degrees 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) angstrom, smaller than corresponding values for stoichiometric imides. This is a kind of 'Li-rich and H-poor' in-tide, which is characteristic of imides by dehydrogenation under LiH-rich conditions. (c) 2007 Elsevier B.V. All rights reserved.