Synthesis of Platinum-Group Metal Nitride OsNx through High-Pressure Coupling Reaction

Platinum-group metals (PGMs) nitrides are a new class of super incompressible superhard materials, which are usually synthesized at high temperatures and pressures (＞45 GPa, 2000 K) with the help of laser-heated diamond anvil cell (LHDAC) technology through the monatomic elemental chemistry reaction method (A+B=AB), and the exploration of non-conventional chemical synthesis methods with effective reduction of the synthesis pressures is of great significance for the development and utilization of PGMs nitrides. In this work, OsNx (x = 0.16-0.38) was synthesized for the first time through a novel high-pressure coupling (HPC) reaction using Fe2O3/Co2O3, hBN, and Os powders as the reaction precursors under high-temperature and high-pressure conditions (15 GPa, 1800-2100 K) provided by a large-volume chamber press. The metal bulk products synthesized through HPC reaction are generally bulk alloys of OsNx compounded with iron-based nitrides. Characterization of the phase composition and structure of the bulk alloy product was conducted using micro-area X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the HPC reaction can synthesize OsNx with a hexagonal OsN2 structure (space group P63/mmc) as predicted by theory, under conditions significantly below the pressure threshold of 50 GPa required for high-pressure monatomic elemental chemistry reaction. The nitrogen atoms partially occupy interstitial lattice sites within the Os crystal. This work shows that the HPC reaction can effectively reduce the energy barrier of metal Os nitration to form non-stoichiometric OsNx compounds, which opens up a new synthetic route for the preparation of platinum-group metals nitrides bulk materials under low-pressure conditions.