Structural, phase stability, electronic, elastic properties and hardness of IrN2 and zinc blende IrN: First-principles calculations

First-principle calculations were performed to investigate the structural, phase stability, electronic, elastic properties and hardness of monoclinic structure IrN2 (m-IrN2), orthorhombic structure IrN2 (o-IrN2) and zinc blende structure IrN (ZB IrN). The results show us that only m-IrN2 is both thermodynamic and dynamic stability. The calculated band structure and density of states (DOS) curves indicate that o-IrN2 and ZB Ir-N compounds we calculated have metallic behavior while m-IrN2 has a small band gap of ~0.3 eV, and exist a common hybridization between Ir-5d and N-2p states, which forming covalent bonding between Ir and N atoms. The difference charge density reveals the electron transfer from Ir atom to N atom for three Ir-N compounds, which forming strong directional covalent bonds. Notable, a strong N-N bond appeared in m-IrN2 and o-IrN2. The ratio of bulk to shear modulus (B/G) indicate that three Ir-N compounds we calculated are ductile, and ZB IrN possesses a better ductility than two types IrN2. m-IrN2 has highest Debye temperature (736 K), illustrating it possesses strongest covalent bonding. The hardness of three Ir-N compounds were also calculated, and the results reveal that m-IrN2 (18.23 GPa) and o-IrN2 (18.02 GPa) are ultraincompressible while ZB IrN has a negative value, which may be attributed to phase transition at ca. 1.98 GPa.