Synthesis of ternary nitrides by mechanochemical alloying

Ternary metal nitrides (of general formula MxM′yNz) attract considerable interest because of their special mechanical, electrical, magnetic, and catalytic properties. Usually they are prepared by ammonolysis of ternary oxides (MxM′yOm) at elevated temperatures. We show that ternary transition metal nitrides are also obtained by nitridation of the corresponding ternary carbide at 823 K. This transformation appears to occur by solid-state diffusion of carbide and nitride ions. To establish more general synthesis schemes for ternary nitrides, we have focused on the preparation of ternary nitrides by mechanochemical alloying of a binary transition metal nitride (MxN) with an elemental transition metal. In this way, we have been able to prepare Fe3Mo3N and Co3Mo3N by ball-milling of Mo2N with Fe and Co, respectively. The transformation sequence from the starting materials (the binary nitride and the transition metal) to the ternary nitride was followed by Mössbauer spectroscopy (for Fe3Mo3N) and by X-ray powder diffraction (for both Fe3Mo3N and Co3Mo3N). Usually, the preparation of a given ternary nitride by ammonolysis of a ternary oxide is dependent on the availability of an oxide precursor with the desired stoichiometric ratio of the two metals. In the present mechanochemical approach, this is not a prerequisite. These synthesis routes are expected to be applicable to the synthesis of a wide range of ternary compounds.