Structural, mechanical, and electronic properties of TaB2TaB2, TaB, IrB2IrB2, and IrB: First-principle calculations

First-principle calculations were performed to investigate the structural, elastic, and electronic properties of TaB2TaB2, TaB, IrB2IrB2, and IrB. The calculated equilibrium structural parameters, shear modulus, and Young's modulus of TaB2TaB2 are well consistent with the available experimental data, and TaB2TaB2 with P6/mmmP6/mmm space group has stronger directional bonding between ions than WB2WB2, OsB2OsB2, IrN2IrN2, and PtN2PtN2. For TaB2TaB2, the hexagonal P6/mmmP6/mmm structure is more stable than the orthorhombic Pmmn   one, while for IrB2IrB2 the orthorhombic Pmmn   structure is the most stable one. The high shear modulus of P6/mmmP6/mmm phase TaB2TaB2 is mainly due to the strong covalent ππ-bonding of B-hexagon in the (0001) plane. Such a B-hexagon network can strongly resist against an applied [112¯0] (0001) shear deformation. Correlation between the hardness and the elastic constants of TaB2TaB2 was discussed. The band structure shows that P6/mmmP6/mmm phase TaB2TaB2 and Pmmn   phase IrB2IrB2 are both metallic. The calculations show that both TaB and IrB are elastically stable with the hexagonal P63/mmcP63/mmc structure.

Elastic constant c44c44 of TaB2TaB2 is calculated to be 235 GPa. This value is exceptionally high, exceeding those of WB2WB2, OsB2OsB2, WB4WB4, OsN2OsN2, IrN2IrN2, and PtN2PtN2.Figure optionsDownload full-size imageDownload as PowerPoint slide