Crystal structures and elastic properties of superhard Ir N 2 and Ir N 3 from first principles

First principles calculations were performed to investigate the structural, elastic, and electronic properties of $\mathrm{Ir}{\mathrm{N}}_{2}$ for various space groups: cubic $Fm\text{\ensuremath{-}}3m$ and $Pa\text{\ensuremath{-}}3$, hexagonal $P{3}_{2}21$, tetragonal $P{4}_{2}∕mnm$, orthorhombic $Pmmn$, $Pnnm$, and $Pnn2$, and monoclinic $P{2}_{1}∕c$. Our calculation indicates that the $P{2}_{1}∕c$ phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of $1.414\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. These characters are consistent with the experimental facts that…

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  National Natural Science Foundation of China