<i>Ab initio</i>study of monoclinic iridium nitride as a high bulk modulus compound

Abstract

The first-principles calculations were performed for various structures of $\mathrm{Ir}{\mathrm{N}}_{2}$ as candidates of the new phase which was recently synthesized under high pressure. It was found that the monoclinic structure is the most stable and shows higher bulk modulus than pyrite $\mathrm{Pt}{\mathrm{N}}_{2}$. The simulated x-ray diffraction pattern agrees well with the experimental one. The positive formation energy of monoclinic $\mathrm{Ir}{\mathrm{N}}_{2}$ indicates that high-pressure is a necessary condition for synthesizing it. The band structure shows that monoclinic $\mathrm{Ir}{\mathrm{N}}_{2}$ is an insulator. The insulating behavior is mainly due to the dimerization of the Ir atoms, which lifts antibonding states formed by Ir $d$ orbitals.