Nitrogen-Rich Molybdenum Nitride Synthesized in a Crucible under Air

The triple bond in N₂ is significantly stronger than the double bond in O₂, meaning that synthesizing nitrogen-rich nitrides typically requires activated nitrogen precursors, such as ammonia, plasma-cracked atomic nitrogen, or high-pressure N₂. Here, we report a synthesis of nitrogen-rich nitrides under ambient pressure and atmosphere. Using Na₂MoO₄ and dicyandiamide precursors, we synthesized nitrogen-rich γ-Mo₂N₃ in an alumina crucible under an ambient atmosphere, heated in a box furnace between 500 and 600 °C. Byproducts of this metathesis reaction include volatile gases and solid Na(OCN), which can be washed away with water. X-ray diffraction and neutron diffraction showed Mo₂N₃ with a rock salt structure having cation vacancies, with no oxygen incorporation, in contrast to the more common nitrogen-poor rock salt Mo₂N with anion vacancies. Moreover, an increase in temperature to 700 °C resulted in molybdenum oxynitride, Mo_0.84N_0.72O_0.27. This work illustrates the potential for dicyandiamide as an ambient-temperature metathesis precursor for an increased effective nitrogen chemical potential under ambient conditions. The classical experimental setting often used for solid-state oxide synthesis, therefore, has the potential to expand the nitride chemistry.