Structural stabilities, elastic and electronic properties of chromium tetraboride from first-principles calculations

Abstract

First-principles calculations are employed to investigate the structural and elastic properties, formation enthalpies and chemical bonding features as well as hardness values of chromium tetraboride [Formula: see text] with different structures. The lattice parameters, Poisson’s ratio and [Formula: see text] ratio are also derived. Our calculations indicate that the orthorhombic structure with Pnnm symmetry is the most energetically stable one for CrB4. Except for [Formula: see text] structure with imaginary frequencies, another six new structures are investigated through the full phonon dispersion calculations. Their mechanical and thermodynamic stabilities are also studied by calculating the elastic constants and formation enthalpies. Our calculations show that the thermodynamic stabilities of all these [Formula: see text] phases can be enhanced under high pressure. The large shear moduli, Young’s moduli and hardness values indicate that these [Formula: see text] phases are potential hard materials. Analyses of the densities of states (DOSs) and electron localization functions (ELFs) provide further understandings of the chemical and physical properties of these [Formula: see text] phases. It is observed that the large occupations and high strengths of the B–B covalent bonds are important for the stabilities, incompressibility and hardnesses of these [Formula: see text] phases.

Electric field manipulation of multiple nonequivalent Dirac cones in the electronic structures of hexagonal CrB 4 sheet

“…[17,18] Just like most 2D materials, this structure with monolayer boron honeycombs possesses single equivalent Dirac cone in the first Brillouin zone. To date, as far as we know, electric structures with multiple nonequivalent Dirac cones have been found only in stable boron bilayers with sandwiched group VI-B elements (molybdenum, [19] chromium, [20] or wolfram [21] ).…”