Composition dependence of hydrogen and ammonia release in the lithium-boron-nitrogen-hydrogen quaternary system

The new quaternary hydride in the lithium-boron-nitrogen-hydrogen (Li-B-N-H) quaternary phase diagram forms by the reaction of lithium amide (LiNH$_{2})$ and lithium borohydride (LiBH$_{4})$ near the approximate composition LiB$_{0.33}$N$_{0.67}$H$_{2.67}$. When heated, the quaternary hydride first melts and then releases greater than 10 wt{\%} hydrogen and a small amount of ammonia (2-3 mole{\%} of the generated gas). We studied hydrogen and ammonia release from the series of reactant mixtures (LiNH$_{2})_{x}$(LiBH$_{4})_{1-x}$ as a function of composition using volumetric, gravimetric, mass spectrometer, and \textit{in situ} x-ray diffraction measurements. We found that maximum hydrogen and minimum ammonia release do occur for x = 0.67. We observe that this composition corresponds to the ternary decomposition end product Li$_{3}$BN$_{2}$ rather than to the true single phase composition of the quaternary hydride as determined from our single crystal x-ray diffraction measurements.