Phase stability, electronic structure and mechanical properties of IrBx (x = 0.9, 1.1): First-principles calculations

• The hexagonal structure of IrB0.9 is more stable than its orthorhombic one.
• The bonding characteristic be directly reflected in total charge density.
• The Debye temperature shows the bond strength of IrB0.9 with different structure.
• The ratio of B/G indicates IrB0.9 with hexagonal and orthorhombic are ductile.

The first-principles calculations based on density functional theory (DFT) are adopted to investigate the phase stability, electronic structure and mechanical properties of IrBx (x = 0.9, 1.1). The formation enthalpy and cohesive energy show that these Iridium borides may be thermodynamically stable, but the phonon calculations show that only IrB0.9 are stable both thermodynamically and dynamically. The calculated electronic structure indicate that they have metallic behavior, and exist a common hybridization between Ir-d and B-p states near the Fermi level, which forming covalent bonding between Ir and B atoms. The total charge density show us the nature of the bond, compared with IrB0.9 with hexagonal structure, orthorhombic structure has strongly B–B bonds, for IrB1.1, there are two types of B–B covalent bonds. The elastic properties of these borides were calculated, which included bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio, the ratio of the bulk modulus to shear modulus (B/G) indicate that both of IrB0.9 in our work are ductile. For IrB0.9, orthorhombic structure has a higher Debye temperature (348 K) than hexagonal structure (251 K). The negative values of C44 and C66 show that IrB1.1 has an unstable structure in mechanical stability.

Total charge density 3D distribution maps of IrB0.9 with hexagonal structure, IrB0.9 with orthorhombic structure and IrB1.1, respectively.Figure optionsDownload as PowerPoint slide