Synthesis of Novel Transition Metal Nitrides ${\mathrm{IrN}}_2$ and ${\mathrm{OsN}}_2$

Two new transition metal nitrides, ${\mathrm{IrN}}_2$ and ${\mathrm{OsN}}_2$, were synthesized at high pressures and temperatures using laser-heated diamond-anvil cell techniques. Synchrotron x-ray diffraction was used to determine the structures of novel nitrides and the equations of states of both the parent metals as well as the newly synthesized materials. The compounds have bulk moduli comparable with those of the traditional superhard materials. For ${\mathrm{IrN}}_2$, the measured bulk modulus [$K_0=428(12)\mathrm{GPa}$] is second only to that of diamond ($K_0=440\mathrm{GPa}$). Ab initio calculations indicate that both compounds have a metal:nitrogen stoichiometry of $1:2$ and that nitrogen intercalates in the lattice of the parent metal in the form of single-bonded N-N units.

Figure 1

X-ray diffraction patterns for the $\mathrm{Ir}+{\mathrm{IrN}}_2$ experiment at 64 GPa (upper curves) and of the $\mathrm{Os}+{\mathrm{OsN}}_2$ experiment at 43 GPa (lower curves). Gray line: LeBail refinement fit [28]; gray crosses: data; upright dashes: predicted reflections. In the case of the $\mathrm{Ir}+{\mathrm{IrN}}_2$ experiment, the spectrum is largely dominated by the Ir signal (ratio $1/100$), which was therefore cut for clarity. Also shown is the difference curve between data and fit.

Figure 2

Equation of state of Ir, Os, IrN, OsN, ${\mathrm{IrN}}_2$, and ${\mathrm{OsN}}_2$. Volume per atom for the observed metal nitrides compared with the volume of the reactants (one atom of $\mathrm{\text{metal}}+{\mathrm{N}}_2$) at room temperature. Solid circles: Experimental data points. Note that the equation of state of Ir is undistinguishable at this scale with that of ${\mathrm{IrN}}_2$ if indexed with $R\overline{3}c$ large cell.

Figure 3

Representative Raman spectra of ${\mathrm{IrN}}_2$ under pressure.