Pressure-dependent deuterium reaction pathways in the Li-N-D system

Neutron diffraction data from in situ deuteration and dedeuteration of Li₃N are presented under different pressure regimes, whereby reaction pathways differing from the widely reported stoichiometric pathway of Li ₃N + 2D₂ ↔ Li₂ND + LiD + D₂ ↔ LiND₂ + 2LiD are observed. At sufficiently high pressures, where the deuterium chemical potential is comparable with the heat of amide formation, the reaction appears to be driven straight to the amide plus deuteride phase mixture. At lower pressures, a cubic phase exhibiting a concentration-dependent variation in lattice parameter is observed. In dedeuteration, two sets of reflections from cubic structures with distinct lattice parameters are observed, both of which exhibit a continual decrease in cell volume. The reaction pathways are discussed in terms of the compositional variation.