Elastic anisotropy of OsB2 and RuB2 from first-principles study

The elastic anisotropy of the potential low compressible and hard materials OsB2 and RuB2 were studied by first-principles investigation within density functional theory. The structure, elastic constants, bulk modulus, shear modulus, Poisson's ratio and Debye temperature have been calculated within both local density approximation (LDA) and generalized gradient approximation (GGA). The results indicated that the calculated bulk modulus and shear modulus were in good agreement with the experimental and previous theoretical studies.

Trends in elasticity and electronic structure of 5d transition metal diborides: first-principles calculations

We investigate the cohesive energy, heat of formation, elastic constant and electronic band structure of transition metal diborides TMB2 (TM = Hf, Ta, W, Re, Os and Ir, Pt) in the Pmmn space group using the ab initio pseudopotential total energy method. Our calculations indicate that there is a relationship between elastic constant and valence electron concentration (VEC): the bulk modulus and shear modulus achieve their maximum when the VEC is in the range of 6.8-7.2. In addition, trends in the elastic constant are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level, which determines the cohesive energy and elastic properties. The maximum in bulk modulus and shear modulus is attributed to the nearly complete filling of TM d-B p bonding states without filling the antibonding states. On the basis of the observed relationship, we predict that alloying W and Re in the orthorhombic structure OsB2 might be harder than alloying the Ir element. Indeed, the further calculations confirmed this expectation.

Low-compressibility and hard materials ReB2 and WB2: Prediction from first-principles study

First-principle calculations are performed to investigate the structural, elastic, and electronic properties of ReB2 and WB2. The calculated equilibrium structural parameters of ReB2 are consistent with the available experimental data. The calculations indicate that WB2 in the P6(3)/mmc space group is more energetically stable under the ambient condition than in the P6/mmm. Based on the calculated bulk modulus, shear modulus of polycrystalline aggregate, ReB2 and WB2 can be regarded as potential candidates of ultra-incompressible and hard materials. Furthermore, the elastic anisotropy is discussed by investigating the elastic stiffness constants. Density of states and electron density analysis unravel the covalent bonding between the transition metal atoms and the boron atoms as the driving force of the high bulk modulus and high shear modulus as well as small Poisson's ratio.