The electronic structure, mechanical and thermodynamic properties of Mo2XB2 and MoX2B4 (X = Fe, Co, Ni) ternary borides

Abstract

The mechanical properties, electronic structure and thermodynamic properties of the Mo2XB2 and MoX2B4 (X = Fe, Co, Ni) ternary borides were calculated by first-principles methods. The elastic constants show that these ternary borides are mechanically stable. Formation enthalpy of Mo2XB2 and MoX2B4 (X = Fe, Co, Ni) ternary borides are at the range of −118.09 kJ/mol to −40.14 kJ/mol. The electronic structures and chemical bonding characteristics are analyzed by the density of states. Mo2FeB2 has the largest shear and Young's modulus because of its strong chemical bonding, and the values are 204.3 GPa and 500.3 GPa, respectively. MoCo2B4 shows the lowest degree of anisotropy due to the lack of strong direction in the bonding. The Debye temperature of MoFe2B4 is the largest among the six phases, which means that MoFe2B4 possesses the best thermal conductivity. Enthalpy shows an approximately linear function of the temperature above 300 K. The entropy of these compounds increase rapidly when the temperature is below 450 K. The Gibbs free energy decreases with the increase in temperature. MoCo2B4 has the lowest Gibbs free energy, which indicates the strongest formation ability in Mo2XB2 and MoX2B4 (X = Fe, Co, Ni) ternary borides.