We report on in situ neutron diffraction measurements during the deuteration of Li3N. A number of novel observations are described: The presence of cubic 'quasi-imide' phases with composition-dependent lattice parameters, the identification of Li4ND and the suppression of LiD formation at low deuterium content. On the basis of these observations, it is proposed that the quasi-imide phase is intermediate between Li4ND and Li2ND, having a composition Li2+yND. Charge balance is accomplished in this compound by the inclusion of both, formally, D-and D+, the latter species being present in the imide ion, (ND)(2-). (c) 2007 Elsevier B.V. All rights reserved.