Pressure-induced structural transition of OsN ₂ and effect of metallic bonding on its hardness

Abstract

Using first-principles calculations, the elastic constant, structural phase transition and effect of metallic bonding on the hardness of OsN2 under high pressure are investigated by means of the pseudopotential plane-waves method. Five candidate structures are chosen to investigate for OsN2, namely, the pyrite, CoSb2-type, marcasite, simple hexagonal and tetragonal structures. A comparison among the formation energies of OsN2 explains the synthesis of OsN2 marcasite under high pressure. On the basis of the third-order Birch-Murnaghan equation of states, the transition pressure Pt (Pt = 223 GPa) between the marcasite and simple tetragonal phase is determinated. Elastic constants, shear modulus, Young's modulus, Poisson's ratio and Debye temperature are derived. The calculated values are, generally speaking, in good agreement with experiments and other theoretical calculations. Our calculation indicates that the N-N bond length is one determinative factor for the ultrahigh bulk moduli of the heavy-transition-metal dinitrides. Moreover, based on Mulliken overlap population analysis in first-principles technique, a semiempirical method to evaluate the hardness of multicomponent crystals with partial metallic bonding is presented. The effect of metallic bonding on the hardness of OsN2 is investigated and the hardness shows a gradual decrease rather than increase under compression, which is different from diamond. This is a quantitative investigation on the structural properties of OsN2, and it still awaits experimental confirmation.

Physical properties of osmium dinitride with fluorite, pyrite, marcasite, and monoclinic structures under high pressure: First-principles study

“…From our analysis, OsN 2 possesses high elastic anisotropy under pressure, and pressure can enhance the ductility of this material. Moreover, the TDOS calculations show that OsN 2 in all structures presents a metallic character, in agreement with previous theoretical results [7,10,[17][18][19]. The sound velocity and thermodynamic properties under diverse pressures of OsN 2 in the four structures have been also investigated successfully.…”

“…Moreover, most theoretical investigations have also focused on the electronic properties of OsN 2 [5,10,12,17], indicating that OsN 2 with marcasite, pyrite and fluorite structures all present a metallic state by first-principles calculations. In 2011, Wang et al [18] investigated the hardness of OsN 2 by analyzing mulliken overlap population, which indicated the marcasite OsN 2 is an ultraincompressible material, in good agreement with the results of refs. 2,5,18.…”

“…In 2011, Wang et al [18] investigated the hardness of OsN 2 by analyzing mulliken overlap population, which indicated the marcasite OsN 2 is an ultraincompressible material, in good agreement with the results of refs. 2,5,18. It is noteworthy that most earlier studies showed that marcasite structure was the most stable phase among three structure types (marcasite, pyrite, and fluorite structures) for OsN 2 [7,10,[12][13][14].…”

“…Many fundamental problems for OsN 2 under ambient conditions, such as the structural, electronic, and elastic properties have been studied extensively [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In 2006, Fan et al [7] studied the structural and elastic properties of pyrite and fluorite structures using first-principles calculations.…”

Structure, mechanical, electronic, and thermodynamic properties of marcasite‐structure TMN2 (TM = Ru, Rh, Os, and Ir) under high pressure: A first‐principles study

“… ( a = 3.944 Å, b = 4.899 Å, c = 2.972 Å). For OsN 2 , X‐ray diffraction patterns can be indexed as orthorhombic, with a = 4.102 Å, b = 4.910 Å, c = 2.714 Å ; our calculated lattice parameters ( a = 4.140 Å, b = 4.941 Å, c = 2.695 Å) match well with theoretical values and the above experimental data . Since orthorhombic IrN 2 has not been synthesized, there is no reliable experimental data that can be used to compare.…”