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,
Mo0.84N0.72O0.27. 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.