To search for a novel transition metal boride superhard material, the structural configuration, hardness and bonding state of the boron rich TiB tetraborides are studied using the first-principles method. Similar to the TMB tetraboride, four tetraborides, orthorhombic (), orthorhombic (), tetragonal (4/) and hexagonal (63/) phases, are predicted based on the phonon dispersion and thermodynamic model. The stable TiB with orthorhombic ( and ) is first predicted. In particular, the theoretical hardness of and TiB is 53.3 GPa and 35.6 GPa, respectively. We predict that orthorhombic () TiB is a potential superhard material. Here, the calculated lattice parameters of the TiB are = 5.2230 Å, = 3.0627 Å and = 9.8026 Å. The calculated lattice parameters of the TiB are = 5.0374 Å, = 5.6542 Å and = 3.0069 Å. Naturally, the high hardness of TiB is related to the octagon B-B cage structure, which is composed of three different B-B covalent bonds. Although the B-B cage structure is formed in TiB, the hard discrepancy is that the bond strength of the B-B covalent bond in TiB is weaker than the bond strength of the B-B covalent bond in TiB. In addition, the Debye temperature of the TiB is higher than those of the other three TiB tetraborides. The high-temperature thermodynamic properties of TiB tetraboride are determined by the vibration in the B atom and B-B covalent bond. Therefore, our study indicates that a novel orthorhombic () TiB superhard material is found.
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http://dx.doi.org/10.1039/d3cp03091a | DOI Listing |
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