Elastic and electronic properties of TcB2 and superhard ReB2:: First-principles calculations

The structural, elastic, and electronic properties of TcB2 and recent synthesized superhard ReB2 were studied by the first-principles calculations. Both ReB2 and TcB2 are found to be elastically stable with the hexagonal and orthorhombic structures. For the two materials, the hexagonal structure is more stable than the orthorhombic one. Moreover, hexagonal ReB2 and TcB2 have stronger directional bonding between ions than OsB2, IrN2, OsN2, and PtN2. The author's calculations show that both ReB2 and TcB2 are potentially superhard materials on the basis of their large bulk moduli and also their large shear to bulk modulus ratios. The band structure shows that experimentally synthesized hexagonal ReB2 is metallic. A pseudogap appears around the Fermi level of the total density of states of hexagonal ReB2, which may contribute to its stability. (c) 2007 American Institute of Physics.