Ammonia is seen as a key part of the transition to a sustainable energy economy, but needs decomposition catalysts to release its stored hydrogen. Lithium nitride-hydride (Li4NH) has been proposed to play a role in the catalytic decomposition of ammonia by non-stoichiometric lithium imide (Li2NH). Although Li4NH is a known decomposition product of Li2NH, it has yet to be observed under ammonia decomposition conditions. Here, we request three days of instrument time on the POLARIS diffractometer to investigate the role of Li4NH in this reaction by i) conducting an in-situ diffraction experiment on chnges to the structure of Li4NH under ammonia decomposition conditions, and ii) exploring the structural transformation between Li2NH and Li4NH by measuring in-situ diffraction data for the thermal decomposition of Li2NH to Li4NH under vacuum.