First-principles investigation on crystal structure and physical properties of HfB4

Abstract Applying the evolutionary algorithm for crystal structure prediction and first-principles calculations, a newly orthorhombic Cmcm structure of HfB 4 is predicted theoretically. The result shows that this new phase is much more superior to the early proposed YB 4 -, ReP 4 -, FeB 4 -, CrB 4 -, and MnB 4 -type structures. The calculations of the phonon dispersion curve and elastic constants verify that the predicted Cmcm phase is dynamically and mechanically stable. Moreover, the predicted large shear modulus (240 GPa) and high hardness (45.7 GPa) imply that the Cmcm -HfB 4 phase is a potential superhard material. At the same time, the dependences of the Young's modulus, bulk modulus, and shear modulus for HfB 4 on the crystal orientation are also systematically studied. Further analyses of the electronic structure and chemical bonding properties indicate that the strong B B and B Hf covalent bonds make great contributions to its high hardness and stability.