Crystal structure and physical properties of ${\mathrm{OsN}}_{2}$ and ${\mathrm{PtN}}_{2}$ in the marcasite phase

Crystal structure and physical properties of ${OsN}_{2}$ and ${PtN}_{2}$ in the marcasite phase

Z. W. Chen, X. J. Guo, Z. Y. Liu, M. Z. Ma, Q. Jing, G. Li, X. Y. Zhang, L. X. Li, Q. Wang, Y. J. Tian, and R. P. Liu

Phys. Rev. B 75, 054103 – Published 6 February 2007

Abstract

We have theoretically evaluated a recently synthesized ${OsN}_{2}$ that was shown to have a large bulk modulus, and we propose a structure that is isostructural with marcasite with the space group Pnnm. The calculated lattice constants, bulk modulus, and x-ray diffraction spectrum of ${OsN}_{2}$ are in good agreement with the experimental results. Calculations of bulk modulus and hardness indicate that the marcasite-type ${OsN}_{2}$ is an ultraincompressible material instead of a superhard one. The possibility of the marcasite ${PtN}_{2}$ has also been investigated, showing that the marcasite ${PtN}_{2}$ could exist as a metastable phase at pressures up to $50 GPa$ , being elastically stable with a slightly higher energy ( $32 meV ∕ atom$ at $0.1 MPa$ ) than that in the pyrite structure.