Self-Combustion Synthesis of Novel Metastable Ternary Molybdenum Nitrides

Ternary metal nitrides are a promising class of functional materials, but their variety has been limited by the challenging nature of nitride synthesis. Here, we demonstrate a facile self-combustion synthesis route to novel ternary molybdenum nitrides. The room temperature mixing of NaNH<sub>2</sub>, MoCl<sub>4</sub>, and 3d transition metal chlorides, such as MnCl<sub>2</sub>, FeCl<sub>2</sub>, and CoCl<sub>2</sub>, initiates a highly exothermic metathesis reaction, which is thermodynamically driven by the formation of stable NaCl, N<sub>2</sub>, and NH<sub>3</sub> byproducts. The rapid combustion reaction yields ternary rocksalt γ-TM<sub>x</sub>Mo<sub>1-x</sub>N<sub>0.5</sub> nanoparticles (TM = Mn, Fe, Co) in just a few seconds. We calculate from DFT that these disordered ternary molybdenum nitrides are thermodynamically stable under the high-temperatures at which they form but are remnantly metastable when quenched to ambient conditions. Introduction of Mn, Fe, and Co into γ-Mo<sub>2</sub>N is found to change its magnetic properties and to enhance its oxygen reduction catalytic activities. Furthermore, our work demonstrates self-combustion synthesis as a simple but powerful route for the realization of novel ternary intermetallic nitrides with emergent functionality.