Investigation of thermodynamic stability, mechanical and electronic properties of superhard tetragonal B4CO4 compound: Ab initio calculations

The density functional theory (DFT) is employed to systematically investigate the structural, elastic, thermal properties, electronic structure and chemical bonding nature of the predicted superhard tetragonal B4CO4 (t-B4CO4). The estimated values of the elastic constants yield mechanical stability of this compound. The large values of bulk modulus (B), shear modulus (G), Young's modulus (E), Vickers hardness (Hv), small Pugh's modulus and Poisson's ratio identify this compound as a possible candidate for superhard material. The thermodynamic properties of t-B4CO4 are predicted for the first time through the quasi-harmonic Debye model where the lattice vibrations are taken into account. The variations of bulk modulus, Debye temperature, specific heats, and volume thermal expansion coefficient with temperature and pressure are successfully achieved for the first time. Predicted large values of Debye and melting temperatures anticipate the possibility of the strong microhardness of this compound. The analysis of electronic density of states and Mulliken populations emphasize the strong covalent bonding of BC (BO) atoms which can be attributed to the mechanism of superhardness of t-B4CO4.