Elastic anisotropy and thermodynamic properties of chromium tetraboride from first-principles calculations

Abstract

First-principles calculations are performed to investigate the elastic anisotropy, and thermodynamic properties of chromium tetraboride (CrB4) under extreme P-T conditions. The calculated equilibrium lattice and the normalized crystal parameters as a function of pressure are in good agreement with the available experimental and theoretical data. Elastic constants Cij are calculated in the pressure range of 0-50GPa, and the bulk modulus B, shear modulus G, and Young's modulus E are also obtained according to the Voigt-Reuss-Hill (VRH) approximation. Anisotropic indexes are employed to characterize the mechanical anisotropy. The bulk modulus and Young's modulus as a function of crystal orientations are also investigated. The obtained results suggest that CrB4 exhibits a pronounced elastic anisotropy. It is strongest along the b-axis in response to compression loading, and the {100} and {001} shear planes might be the cleavage planes. The elastic anisotropy of CrB4 may possibly limit its applications. Using the quasiharmonic Debye model, thermodynamic properties like Debye temperature, Grüneisen parameter, heat capacity, and expansion coefficient are also systematically explored under extreme P-T conditions.