Two-step solid-state synthesis of ternary nitride materials

TL;DR

This paper introduces a simple two-step solid-state synthesis method for ternary nitrides using ion-exchange reactions, enabling the production of phase-pure materials without high-pressure or reactive gases.

Contribution

The study demonstrates a novel two-step synthesis process for ternary nitrides that avoids complex equipment, providing a new route for discovering bulk ternary nitride materials.

Findings

Successful synthesis of MgZrN₂, Mg₂NbN₃, and MgMoN₂ with phase purity.

Low-temperature step promotes Mg-M-N bond formation.

High-temperature annealing increases crystalline domain size.

Abstract

Ternary nitride materials hold promise for many optical, electronic, and refractory applications yet their preparation via solid-state synthesis remains challenging. Often, high pressures or reactive gasses are used to manipulate the effective chemical potential of nitrogen, yet these strategies require specialized equipment. Here we report on a simple two-step synthesis using ion-exchange reactions that yield rocksalt-derived MgZrN$_2$ and Mg$_2$NbN$_3$, as well as layered MgMoN$_2$. All three compounds show nearly temperature-independent and weak paramagnetic responses to an applied magnetic field at cryogenic temperatures indicating phase pure products. The key to synthesizing these ternary materials is an initial low-temperature step (300-450 $^{\circ}$C) to promote Mg-M-N bond formation. Then the products are annealed (800-900 $^{\circ}$C) to increase crystalline domains of the ternary product. Calorimetry experiments reveal that initial reaction temperatures are determined by phase transitions of reaction precursors, whereas heating directly to high temperatures results in decomposition. These two-step reactions provide a rational guide to material discovery of other bulk ternary nitrides.