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

Platinum-group metals (PGMs) nitrides represent a new class of super incompressible superhard materials, typically synthesized under extreme conditions (above 45 GPa, 2000 K) using laser-heated diamond anvil cell (LHDAC) technology via monatomic elemental chemosynthesis (A+B=AB). Exploring non-conventional synthesis methods that significantly reduce the required pressures is crucial for advancing the development and application of PGMs nitrides. In this work, OsN_x (0.16≤x≤0.38) was synthesized for the first time via a novel high-pressure coupling (HPC) reaction, using Fe₂O₃/Co₂O₃, h-BN, and Os powders as precursors under high-temperature and high-pressure conditions (15 GPa, 1800−2100 K) in a large-volume press. The HPC-synthesized metal bulk products primarily consist of OsN_x alloyed with iron-based nitrides. Phase composition and structural characterization via X-ray powder diffraction (XRD) and scanning electron microscope (SEM) confirm the formation of hexagonal OsN₂ (space group P6₃/mmc), as theoretically predicted, at pressures well below the 50 GPa threshold typically required for high-pressure monatomic elemental combination reactions. The nitrogen atoms partially occupy interstitial sites within the Os crystal structure. This study demonstrates that the HPC reaction effectively lowers the energy barrier for Os nitration, facilitating the formation of non-stoichiometric OsN_x compounds. These findings open a new synthetic route for bulk PGM nitride materials under significantly reduced pressure conditions.