Bulk synthesis of Zn${}_3$WN${}_4$ via solid-state metathesis

Abstract

Ternary nitrides are of growing technological importance, with applications as semiconductors, catalysts, and magnetic materials; however, new synthetic tools are needed to advance materials discovery efforts. Here, we show that Zn${}_3$WN${}_4$ can be synthesized via metathesis reactions between Li${}_6$WN${}_4$ and Zn$X_2$ ($X$ = Br, Cl, F). In situ synchrotron powder X-ray diffraction and differential scanning calorimetry show that the reaction onset is correlated with the Zn$X_2$ melting point and that product purity is inversely correlated with the reaction's exothermicity. High resolution synchrotron powder X-ray diffraction measurements show that this bulk synthesis produces a structure with substantial cation ordering, as opposed to the disordered structure initially discovered via thin film sputtering. Diffuse reflectance spectroscopy reveals that Zn${}_3$WN${}_4$ powders exhibit two optical absorption onsets at 2.5 eV and 4.0 eV, indicating wide-bandgap semiconducting behavior and suggesting a small amount of structural disorder. We hypothesize that this synthesis strategy is generalizable because many potential Li-$M$-N precursors (where $M$ is a metal) are available for synthesizing new ternary nitride materials. This work introduces a promising synthesis strategy that will accelerate the discovery of novel functional ternary nitrides and other currently inaccessible materials.