Bulk Synthesis, Structure, and Electronic Properties of Magnesium Zirconium Nitride Solid Solutions

Ternary nitride phase space holds great potential for new functional materials, as suggested by computational predictions of yet-to-be discovered stable phases. Here, we report a metathesis route to bulk powders of MgZrN2 and the solid solutions MgxZr2-xN2 (0 < x < 1). These ternary phases only result when lower temperature reactions are used, in contrast to previous work using the similar Mg-based metathesis reactions that resulted in the formation of exclusively ZrN. Thermochemical calculations illustrate why lower temperature metathesis reactions yield the incorporation of Mg, while higher temperature ceramic reactions yield exclusively ZrN. Experimental in situ X-ray diffraction of metathesis reactions during heating reveals two stages in the reaction pathway: initial consumption of the precursors to make an amorphous product (T-rxn > 350 degrees C) followed by crystallization at higher temperatures (T-rxn > 500 degrees C). Changing the ratio of the metathesis precursors (Mg2NCl and ZrCl4) controllably varies the composition of MgxZr2-xN2, which crystallizes as a cation-disordered rock salt, as evidenced by high-resolution synchrotron X-ray diffraction, electron microscopy, and bulk compositional analysis. Variation in composition leads to a gradual metal-to-insulator transition with increasing x, similar to other reports of analogous thin film specimens produced by combinatorial sputtering. Meanwhile, the optical behavior of these powders suggests nanoscale compositional inhomogeneity, as signatures of ZrN-like absorption are detectable even in Mg-rich samples. This metathesis approach appears to be generalizable to the synthesis of bulk ternary nitride materials.

Automated summary

This study reports the synthesis of bulk powders of MgZrN2 and MgxZr2-xN2 (0 < x < 1) through a metathesis route, showing that lower temperature reactions lead to the formation of these ternary phases instead of exclusively ZrN. Thermochemical calculations suggest that controlling the ratio of metathesis precursors can vary the composition of MgxZr2-xN2, resulting in a gradual metal-to-insulator transition with increasing x. Furthermore, optical behavior indicates nanoscale compositional inhomogeneity in the powders, even in Mg-rich samples.